ScalaTest 3.0.5 - org.scalatest

trait Alerter extends AnyRef

Trait providing an apply method to which alert messages about a running suite of tests can be reported.

An Alerter is essentially used to wrap a Reporter and provide easy ways to send alert messages to that Reporter via an AlertProvided event. Alerter contains an apply method that takes a string and an optional payload object of type Any. The Alerter will forward the passed alert message string to the Reporter as the message parameter, and the optional payload object as the payload parameter, of an AlertProvided event.

For insight into the differences between Alerter, Notifier, and Informer, see the main documentation for trait Alerting.

trait Alerting extends AnyRef

Trait that contains the alert method, which can be used to send an alert to the reporter.

One difference between alert and the info method of Informer is that info messages provided during a test are recorded and sent as part of test completion event, whereas alert messages are sent right away as AlertProvided messages. For long-running tests, alert allows you to send "alert notifications" to the reporter right away, so users can be made aware of potential problems being experienced by long-running tests. By contrast, info messages will only be seen by the user after the test has completed, and are more geared towards specification (such as Given/When/Then messages) than notification.

The difference between alert and the update method of Updating is that alert is intended to be used for warnings or notifications of potential problems, whereas update is just for status updates. In string reporters for which ANSI color is enabled, update notifications are shown in green and alert notifications in yellow.

trait AppendedClues extends AnyRef

Trait providing an implicit conversion that allows clues to be placed after a block of code.

You can use the withClue construct provided by Assertions, which is extended by every style trait in ScalaTest, to add extra information to reports of failed or canceled tests. The withClue from Assertions places the "clue string" at the front, both in the code and in the resulting message:

withClue("This is a prepended clue;") {
  1 + 1 should equal (3)
}

The above expression will yield the failure message:

This is a prepended clue; 2 did not equal 3

If you mix in this trait, or import its members via its companion object, you can alternatively place the clue string at the end, like this:

{ 1 + 1 should equal (3) } withClue "now the clue comes after"

The above expression will yield the failure message:

2 did not equal 3 now the clue comes after

If no space is already present, either at the beginning of the clue string or at the end of the current message, a space will be placed between the two, unless the clue string starts with one of the punctuation characters: comma (,), period (.), or semicolon (;). For example, the failure message in the above example includes an extra space inserted between 3 and now.

By contrast this code, which has a clue string starting with comma:

{ 1 + 1 should equal (3) } withClue ", now the clue comes after"

Will yield a failure message with no extra inserted space:

2 did not equal 3, now the clue comes after

The withClue method will only append the clue string to the detail message of exception types that mix in the ModifiableMessage trait. See the documentation for ModifiableMessage for more information.

Note: the reason this functionality is not provided by Assertions directly, like the prepended withClue construct, is because appended clues require an implicit conversion. ScalaTest only gives you one implicit conversion by default in any test class to minimize the potential for conflicts with other implicit conversions you may be using. All other implicit conversions, including the one provided by this trait, you must explicitly invite into your code through inheritance or an import.

case class Args(reporter: Reporter, stopper: Stopper = Stopper.default, filter: Filter = Filter.default, configMap: ConfigMap = ConfigMap.empty, distributor: Option[Distributor] = None, tracker: Tracker = Tracker.default, chosenStyles: Set[String] = Set.empty, runTestInNewInstance: Boolean = false, distributedTestSorter: Option[DistributedTestSorter] = None, distributedSuiteSorter: Option[DistributedSuiteSorter] = None) extends Product with Serializable

Arguments bundle passed to four of ScalaTest's lifecycle methods: run, runNestedSuites, runTests, and runTest.

The signatures of these methods, defined in trait Suite, are:

def run(testName: Option[String], args: Args)
def runNestedSuites(args: Args)
def runTests(testName: Option[String], args: Args)
def runTest(testName: String, args: Args)

The purpose of bundling these arguments into an Args object instead of passing them in individually is to make the signature of these four lifecycle methods easier to read, write, and remember, as well as to make the methods more pleasant to override in user code.

reporter: the Reporter to which results will be reported
stopper: the Stopper that will be consulted to determine whether to stop execution early.
filter: a Filter with which to filter tests based on their tags
configMap: a ConfigMap of key-value pairs that can be used by the executing Suite of tests.
distributor: an optional Distributor, into which to put nested Suites to be executed by another entity, such as concurrently by a pool of threads. If None, nested Suites will be executed sequentially.
tracker: a Tracker tracking Ordinals being fired by the current thread.
chosenStyles: a (possibly empty) Set of Strings specifying the run's chosen styles
runTestInNewInstance: a flag used to pass information between run methods in OneInstancePerTest and ParallelTestExecution.
distributedTestSorter: an optional DistributedTestSorter used by ParallelTestExecution to sort the events for the parallel-executed tests of one suite back into sequential order on the fly, with a timeout in case a test takes too long to complete
distributedSuiteSorter: an optional DistributedSuiteSorter used by ParallelTestExecution to ensure the events for the parallel-executed suites are sorted back into sequential order, with a timeout in case a suite takes to long to complete, even when tests are executed in parallel

Exceptions thrown: NullArgumentException if any passed parameter is null.

type Assertion = scalatest.compatible.Assertion

trait Assertions extends TripleEquals

Trait that contains ScalaTest's basic assertion methods.

You can use the assertions provided by this trait in any ScalaTest Suite, because Suite mixes in this trait. This trait is designed to be used independently of anything else in ScalaTest, though, so you can mix it into anything. (You can alternatively import the methods defined in this trait. For details, see the documentation for the Assertions companion object.

In any Scala program, you can write assertions by invoking assert and passing in a Boolean expression, such as:

val left = 2
val right = 1
assert(left == right)

If the passed expression is true, assert will return normally. If false, Scala's assert will complete abruptly with an AssertionError. This behavior is provided by the assert method defined in object Predef, whose members are implicitly imported into every Scala source file. This Assertions trait defines another assert method that hides the one in Predef. It behaves the same, except that if false is passed it throws TestFailedException instead of AssertionError. Why? Because unlike AssertionError, TestFailedException carries information about exactly which item in the stack trace represents the line of test code that failed, which can help users more quickly find an offending line of code in a failing test. In addition, ScalaTest's assert provides better error messages than Scala's assert.

If you pass the previous Boolean expression, left == right to assert in a ScalaTest test, a failure will be reported that, because assert is implemented as a macro, includes reporting the left and right values. For example, given the same code as above but using ScalaTest assertions:

import org.scalatest.Assertions._
val left = 2
val right = 1
assert(left == right)

The detail message in the thrown TestFailedException from this assert will be: "2 did not equal 1".

ScalaTest's assert macro works by recognizing patterns in the AST of the expression passed to assert and, for a finite set of common expressions, giving an error message that an equivalent ScalaTest matcher expression would give. Here are some examples, where a is 1, b is 2, c is 3, d is 4, xs is List(a, b, c), and num is 1.0:

assert(a == b || c >= d)
// Error message: 1 did not equal 2, and 3 was not greater than or equal to 4

assert(xs.exists(_ == 4))
// Error message: List(1, 2, 3) did not contain 4

assert("hello".startsWith("h") && "goodbye".endsWith("y"))
// Error message: "hello" started with "h", but "goodbye" did not end with "y"

assert(num.isInstanceOf[Int])
// Error message: 1.0 was not instance of scala.Int

assert(Some(2).isEmpty)
// Error message: Some(2) was not empty

For expressions that are not recognized, the macro currently prints out a string representation of the (desugared) AST and adds "was false". Here are some examples of error messages for unrecognized expressions:

assert(None.isDefined)
// Error message: scala.None.isDefined was false

assert(xs.exists(i => i > 10))
// Error message: xs.exists(((i: Int) => i.>(10))) was false

You can augment the standard error message by providing a String as a second argument to assert, like this:

val attempted = 2
assert(attempted == 1, "Execution was attempted " + left + " times instead of 1 time")

Using this form of assert, the failure report will be more specific to your problem domain, thereby helping you debug the problem. This Assertions trait also mixes in the TripleEquals, which gives you a === operator that allows you to customize Equality, perform equality checks with numeric Tolerance, and enforce type constraints at compile time with sibling traits TypeCheckedTripleEquals and ConversionCheckedTripleEquals.

Expected results

Although the assert macro provides a natural, readable extension to Scala's assert mechanism that provides good error messages, as the operands become lengthy, the code becomes less readable. In addition, the error messages generated for == and === comparisons don't distinguish between actual and expected values. The operands are just called left and right, because if one were named expected and the other actual, it would be difficult for people to remember which was which. To help with these limitations of assertions, Suite includes a method called assertResult that can be used as an alternative to assert. To use assertResult, you place the expected value in parentheses after assertResult, followed by curly braces containing code that should result in the expected value. For example:

val a = 5
val b = 2
assertResult(2) {
  a - b
}

In this case, the expected value is 2, and the code being tested is a - b. This assertion will fail, and the detail message in the TestFailedException will read, "Expected 2, but got 3."

Forcing failures

If you just need the test to fail, you can write:

fail()

Or, if you want the test to fail with a message, write:

fail("I've got a bad feeling about this")

Achieving success

In async style tests, you must end your test body with either Future[Assertion] or Assertion. ScalaTest's assertions (including matcher expressions) have result type Assertion, so ending with an assertion will satisfy the compiler. If a test body or function body passed to Future.map does not end with type Assertion, however, you can fix the type error by placing succeed at the end of the test or function body:

succeed // Has type Assertion

Expected exceptions

Sometimes you need to test whether a method throws an expected exception under certain circumstances, such as when invalid arguments are passed to the method. You can do this in the JUnit 3 style, like this:

val s = "hi"
try {
  s.charAt(-1)
  fail()
}
catch {
  case _: IndexOutOfBoundsException => // Expected, so continue
}

If charAt throws IndexOutOfBoundsException as expected, control will transfer to the catch case, which does nothing. If, however, charAt fails to throw an exception, the next statement, fail(), will be run. The fail method always completes abruptly with a TestFailedException, thereby signaling a failed test.

To make this common use case easier to express and read, ScalaTest provides two methods: assertThrows and intercept. Here's how you use assertThrows:

val s = "hi"
assertThrows[IndexOutOfBoundsException] { // Result type: Assertion
  s.charAt(-1)
}

This code behaves much like the previous example. If charAt throws an instance of IndexOutOfBoundsException, assertThrows will return Succeeded. But if charAt completes normally, or throws a different exception, assertThrows will complete abruptly with a TestFailedException.

The intercept method behaves the same as assertThrows, except that instead of returning Succeeded, intercept returns the caught exception so that you can inspect it further if you wish. For example, you may need to ensure that data contained inside the exception have expected values. Here's an example:

val s = "hi"
val caught =
  intercept[IndexOutOfBoundsException] { // Result type: IndexOutOfBoundsException
    s.charAt(-1)
  }
assert(caught.getMessage.indexOf("-1") != -1)

Checking that a snippet of code does or does not compile

Often when creating libraries you may wish to ensure that certain arrangements of code that represent potential “user errors” do not compile, so that your library is more error resistant. ScalaTest's Assertions trait includes the following syntax for that purpose:

assertDoesNotCompile("val a: String = 1")

If you want to ensure that a snippet of code does not compile because of a type error (as opposed to a syntax error), use:

assertTypeError("val a: String = 1")

Note that the assertTypeError call will only succeed if the given snippet of code does not compile because of a type error. A syntax error will still result on a thrown TestFailedException.

If you want to state that a snippet of code does compile, you can make that more obvious with:

assertCompiles("val a: Int = 1")

Although the previous three constructs are implemented with macros that determine at compile time whether the snippet of code represented by the string does or does not compile, errors are reported as test failures at runtime.

Assumptions

Trait Assertions also provides methods that allow you to cancel a test. You would cancel a test if a resource required by the test was unavailable. For example, if a test requires an external database to be online, and it isn't, the test could be canceled to indicate it was unable to run because of the missing database. Such a test assumes a database is available, and you can use the assume method to indicate this at the beginning of the test, like this:

assume(database.isAvailable)

For each overloaded assert method, trait Assertions provides an overloaded assume method with an identical signature and behavior, except the assume methods throw TestCanceledException whereas the assert methods throw TestFailedException. As with assert, assume hides a Scala method in Predef that performs a similar function, but throws AssertionError. And just as you can with assert, you will get an error message extracted by a macro from the AST passed to assume, and can optionally provide a clue string to augment this error message. Here are some examples:

assume(database.isAvailable, "The database was down again")
assume(database.getAllUsers.count === 9)

Forcing cancelations

For each overloaded fail method, there's a corresponding cancel method with an identical signature and behavior, except the cancel methods throw TestCanceledException whereas the fail methods throw TestFailedException. Thus if you just need to cancel a test, you can write:

cancel()

If you want to cancel the test with a message, just place the message in the parentheses:

cancel("Can't run the test because no internet connection was found")

Getting a clue

If you want more information that is provided by default by the methods if this trait, you can supply a "clue" string in one of several ways. The extra information (or "clues") you provide will be included in the detail message of the thrown exception. Both assert and assertResult provide a way for a clue to be included directly, intercept does not. Here's an example of clues provided directly in assert:

assert(1 + 1 === 3, "this is a clue")

and in assertResult:

assertResult(3, "this is a clue") { 1 + 1 }

The exceptions thrown by the previous two statements will include the clue string, "this is a clue", in the exception's detail message. To get the same clue in the detail message of an exception thrown by a failed intercept call requires using withClue:

withClue("this is a clue") {
  intercept[IndexOutOfBoundsException] {
    "hi".charAt(-1)
  }
}

The withClue method will only prepend the clue string to the detail message of exception types that mix in the ModifiableMessage trait. See the documentation for ModifiableMessage for more information. If you wish to place a clue string after a block of code, see the documentation for AppendedClues.

Note: ScalaTest's assertTypeError construct is in part inspired by the illTyped macro of shapeless.

abstract class AsyncFeatureSpec extends AsyncFeatureSpecLike

Enables testing of asynchronous code without blocking, using a style consistent with traditional FeatureSpec tests.

Recommended Usage: AsyncFeatureSpec is intended to enable users of FeatureSpec to write non-blocking asynchronous tests that are consistent with their traditional FeatureSpec tests. Note: AsyncFeatureSpec is intended for use in special situations where non-blocking asynchronous testing is needed, with class FeatureSpec used for general needs.

Given a Future returned by the code you are testing, you need not block until the Future completes before performing assertions against its value. You can instead map those assertions onto the Future and return the resulting Future[Assertion] to ScalaTest. The test will complete asynchronously, when the Future[Assertion] completes.

Although not required, FeatureSpec is often used together with GivenWhenThen to express acceptance requirements in more detail. Here's an example AsyncFeatureSpec:

package org.scalatest.examples.asyncfeaturespec

import org.scalatest._
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
case object IsOn
case object PressPowerButton

class TVSetActor { // Simulating an actor
  private var on: Boolean = false
  def !(msg: PressPowerButton.type): Unit =
    synchronized {
      on = !on
    }
  def ?(msg: IsOn.type)(implicit c: ExecutionContext): Future[Boolean] =
    Future {
      synchronized { on }
    }
}

class TVSetActorSpec extends AsyncFeatureSpec with GivenWhenThen {

  implicit override def executionContext =
    scala.concurrent.ExecutionContext.Implicits.global

  info("As a TV set owner")
  info("I want to be able to turn the TV on and off")
  info("So I can watch TV when I want")
  info("And save energy when I'm not watching TV")

  feature("TV power button") {
    scenario("User presses power button when TV is off") {

      Given("a TV set that is switched off")
      val tvSetActor = new TVSetActor

      When("the power button is pressed")
      tvSetActor ! PressPowerButton

      Then("the TV should switch on")
      val futureBoolean = tvSetActor ? IsOn
      futureBoolean map { isOn => assert(isOn) }
    }

    scenario("User presses power button when TV is on") {

      Given("a TV set that is switched on")
      val tvSetActor = new TVSetActor
      tvSetActor ! PressPowerButton

      When("the power button is pressed")
      tvSetActor ! PressPowerButton

      Then("the TV should switch off")
      val futureBoolean = tvSetActor ? IsOn
      futureBoolean map { isOn => assert(!isOn) }
    }
  }
}

Note: for more information on the calls to Given, When, and Then, see the documentation for trait GivenWhenThen and the Informers section below.

An AsyncFeatureSpec contains feature clauses and scenarios. You define a feature clause with feature, and a scenario with scenario. Both feature and scenario are methods, defined in AsyncFeatureSpec, which will be invoked by the primary constructor of TVSetActorSpec. A feature clause describes a feature of the subject (class or other entity) you are specifying and testing. In the previous example, the subject under specification and test is a TV set. The feature being specified and tested is the behavior of a TV set when its power button is pressed. With each scenario you provide a string (the spec text) that specifies the behavior of the subject for one scenario in which the feature may be used, and a block of code that tests that behavior. You place the spec text between the parentheses, followed by the test code between curly braces. The test code will be wrapped up as a function passed as a by-name parameter to scenario, which will register the test for later execution. The result type of the by-name in an AsyncFeatureSpec must be Future[Assertion].

Starting with version 3.0.0, ScalaTest assertions and matchers have result type Assertion. The result type of the first test in the example above, therefore, is Future[Assertion]. When an AsyncFeatureSpec is constructed, any test that results in Assertion will be implicitly converted to Future[Assertion] and registered. The implicit conversion is from Assertion to Future[Assertion] only, so you must end synchronous tests in some ScalaTest assertion or matcher expression. If a test would not otherwise end in type Assertion, you can place succeed at the end of the test. succeed, a field in trait Assertions, returns the Succeeded singleton:

scala> succeed
res2: org.scalatest.Assertion = Succeeded

Thus placing succeed at the end of a test body will satisfy the type checker.

An AsyncFeatureSpec's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Scenarios can only be registered with the scenario method while the AsyncFeatureSpec is in its registration phase. Any attempt to register a scenario after the AsyncFeatureSpec has entered its ready phase, i.e., after run has been invoked on the AsyncFeatureSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using AsyncFeatureSpec is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Each scenario represents one test. The name of the test is the spec text passed to the scenario method. The feature name does not appear as part of the test name. In a AsyncFeatureSpec, therefore, you must take care to ensure that each test has a unique name (in other words, that each scenario has unique spec text).

When you run a AsyncFeatureSpec, it will send Formatters in the events it sends to the Reporter. ScalaTest's built-in reporters will report these events in such a way that the output is easy to read as an informal specification of the subject being tested. For example, were you to run TVSetSpec from within the Scala interpreter:

scala> org.scalatest.run(new TVSetActorSpec)

You would see:

TVSetActorSpec:
As a TV set owner
I want to be able to turn the TV on and off
So I can watch TV when I want
And save energy when I'm not watching TV
Feature: TV power button
  Scenario: User presses power button when TV is off
    Given a TV set that is switched off
    When the power button is pressed
    Then the TV should switch on
  Scenario: User presses power button when TV is on
    Given a TV set that is switched on
    When the power button is pressed
    Then the TV should switch off

Or, to run just the “Feature: TV power button Scenario: User presses power button when TV is on” method, you could pass that test's name, or any unique substring of the name, such as "TV is on". Here's an example:

scala> org.scalatest.run(new TVSetActorSpec, "TV is on")
TVSetActorSpec:
As a TV set owner
I want to be able to turn the TV on and off
So I can watch TV when I want
And save energy when I'm not watching TV
Feature: TV power button
  Scenario: User presses power button when TV is on
    Given a TV set that is switched on
    When the power button is pressed
    Then the TV should switch off

Asynchronous execution model

AsyncFeatureSpec extends AsyncTestSuite, which provides an implicit scala.concurrent.ExecutionContext named executionContext. This execution context is used by AsyncFeatureSpec to transform the Future[Assertion]s returned by each test into the FutureOutcome returned by the test function passed to withFixture. This ExecutionContext is also intended to be used in the tests, including when you map assertions onto futures.

On both the JVM and Scala.js, the default execution context provided by ScalaTest's asynchronous testing styles confines execution to a single thread per test. On JavaScript, where single-threaded execution is the only possibility, the default execution context is scala.scalajs.concurrent.JSExecutionContext.Implicits.queue. On the JVM, the default execution context is a serial execution context provided by ScalaTest itself.

When ScalaTest's serial execution context is called upon to execute a task, that task is recorded in a queue for later execution. For example, one task that will be placed in this queue is the task that transforms the Future[Assertion] returned by an asynchronous test body to the FutureOutcome returned from the test function. Other tasks that will be queued are any transformations of, or callbacks registered on, Futures that occur in your test body, including any assertions you map onto Futures. Once the test body returns, the thread that executed the test body will execute the tasks in that queue one after another, in the order they were enqueued.

ScalaTest provides its serial execution context as the default on the JVM for three reasons. First, most often running both tests and suites in parallel does not give a significant performance boost compared to just running suites in parallel. Thus parallel execution of Future transformations within individual tests is not generally needed for performance reasons.

Second, if multiple threads are operating in the same suite concurrently, you'll need to make sure access to any mutable fixture objects by multiple threads is synchronized. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, this does not hold true for callbacks, and in general it is easy to make a mistake. Simply put: synchronizing access to shared mutable state is difficult and error prone. Because ScalaTest's default execution context on the JVM confines execution of Future transformations and call backs to a single thread, you need not (by default) worry about synchronizing access to mutable state in your asynchronous-style tests.

Third, asynchronous-style tests need not be complete when the test body returns, because the test body returns a Future[Assertion]. This Future[Assertion] will often represent a test that has not yet completed. As a result, when using a more traditional execution context backed by a thread-pool, you could potentially start many more tests executing concurrently than there are threads in the thread pool. The more concurrently execute tests you have competing for threads from the same limited thread pool, the more likely it will be that tests will intermitently fail due to timeouts.

Using ScalaTest's serial execution context on the JVM will ensure the same thread that produced the Future[Assertion] returned from a test body is also used to execute any tasks given to the execution context while executing the test body—and that thread will not be allowed to do anything else until the test completes. If the serial execution context's task queue ever becomes empty while the Future[Assertion] returned by that test's body has not yet completed, the thread will block until another task for that test is enqueued. Although it may seem counter-intuitive, this blocking behavior means the total number of tests allowed to run concurrently will be limited to the total number of threads executing suites. This fact means you can tune the thread pool such that maximum performance is reached while avoiding (or at least, reducing the likelihood of) tests that fail due to timeouts because of thread competition.

This thread confinement strategy does mean, however, that when you are using the default execution context on the JVM, you must be sure to never block in the test body waiting for a task to be completed by the execution context. If you block, your test will never complete. This kind of problem will be obvious, because the test will consistently hang every time you run it. (If a test is hanging, and you're not sure which one it is, enable slowpoke notifications.) If you really do want to block in your tests, you may wish to just use a traditional FeatureSpec with ScalaFutures instead. Alternatively, you could override the executionContext and use a traditional ExecutionContext backed by a thread pool. This will enable you to block in an asynchronous-style test on the JVM, but you'll need to worry about synchronizing access to shared mutable state.

To use a different execution context, just override executionContext. For example, if you prefer to use the runNow execution context on Scala.js instead of the default queue, you would write:

// on Scala.js
implicit override def executionContext =
    scala.scalajs.concurrent.JSExecutionContext.Implicits.runNow

If you prefer on the JVM to use the global execution context, which is backed by a thread pool, instead of ScalaTest's default serial execution contex, which confines execution to a single thread, you would write:

// on the JVM (and also compiles on Scala.js, giving
// you the queue execution context)
implicit override def executionContext =
    scala.concurrent.ExecutionContext.Implicits.global

Serial and parallel test execution

By default (unless you mix in ParallelTestExecution), tests in an AsyncFeatureSpec will be executed one after another, i.e., serially. This is true whether those tests return Assertion or Future[Assertion], no matter what threads are involved. This default behavior allows you to re-use a shared fixture, such as an external database that needs to be cleaned after each test, in multiple tests in async-style suites. This is implemented by registering each test, other than the first test, to run as a continuation after the previous test completes.

If you want the tests of an AsyncFeatureSpec to be executed in parallel, you must mix in ParallelTestExecution and enable parallel execution of tests in your build. You enable parallel execution in Runner with the -P command line flag. In the ScalaTest Maven Plugin, set parallel to true. In sbt, parallel execution is the default, but to be explicit you can write:

parallelExecution in Test := true // the default in sbt

On the JVM, if both ParallelTestExecution is mixed in and parallel execution is enabled in the build, tests in an async-style suite will be started in parallel, using threads from the Distributor, and allowed to complete in parallel, using threads from the executionContext. If you are using ScalaTest's serial execution context, the JVM default, asynchronous tests will run in parallel very much like traditional (such as FeatureSpec) tests run in parallel: 1) Because ParallelTestExecution extends OneInstancePerTest, each test will run in its own instance of the test class, you need not worry about synchronizing access to mutable instance state shared by different tests in the same suite. 2) Because the serial execution context will confine the execution of each test to the single thread that executes the test body, you need not worry about synchronizing access to shared mutable state accessed by transformations and callbacks of Futures inside the test.

If ParallelTestExecution is mixed in but parallel execution of suites is not enabled, asynchronous tests on the JVM will be started sequentially, by the single thread that invoked run, but without waiting for one test to complete before the next test is started. As a result, asynchronous tests will be allowed to complete in parallel, using threads from the executionContext. If you are using the serial execution context, however, you'll see the same behavior you see when parallel execution is disabled and a traditional suite that mixes in ParallelTestExecution is executed: the tests will run sequentially. If you use an execution context backed by a thread-pool, such as global, however, even though tests will be started sequentially by one thread, they will be allowed to run concurrently using threads from the execution context's thread pool.

The latter behavior is essentially what you'll see on Scala.js when you execute a suite that mixes in ParallelTestExecution. Because only one thread exists when running under JavaScript, you can't "enable parallel execution of suites." However, it may still be useful to run tests in parallel on Scala.js, because tests can invoke API calls that are truly asynchronous by calling into external APIs that take advantage of non-JavaScript threads. Thus on Scala.js, ParallelTestExecution allows asynchronous tests to run in parallel, even though they must be started sequentially. This may give you better performance when you are using API calls in your Scala.js tests that are truly asynchronous.

Futures and expected exceptions

If you need to test for expected exceptions in the context of futures, you can use the recoverToSucceededIf and recoverToExceptionIf methods of trait RecoverMethods. Because this trait is mixed into supertrait AsyncTestSuite, both of these methods are available by default in an AsyncFeatureSpec.

If you just want to ensure that a future fails with a particular exception type, and do not need to inspect the exception further, use recoverToSucceededIf:

recoverToSucceededIf[IllegalStateException] { // Result type: Future[Assertion]
  emptyStackActor ? Peek
}

The recoverToSucceededIf method performs a job similar to assertThrows, except in the context of a future. It transforms a Future of any type into a Future[Assertion] that succeeds only if the original future fails with the specified exception. Here's an example in the REPL:

scala> import org.scalatest.RecoverMethods._
import org.scalatest.RecoverMethods._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.ExecutionContext.Implicits.global

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new IllegalStateException }
     | }
res0: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res0.value
res1: Option[scala.util.Try[org.scalatest.Assertion]] = Some(Success(Succeeded))

Otherwise it fails with an error message similar to those given by assertThrows:

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new RuntimeException }
     | }
res2: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res2.value
res3: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but java.lang.RuntimeException
      was thrown))

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { 42 }
     | }
res4: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res4.value
res5: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but no exception was thrown))

The recoverToExceptionIf method differs from the recoverToSucceededIf in its behavior when the assertion succeeds: recoverToSucceededIf yields a Future[Assertion], whereas recoverToExceptionIf yields a Future[T], where T is the expected exception type.

recoverToExceptionIf[IllegalStateException] { // Result type: Future[IllegalStateException]
  emptyStackActor ? Peek
}

In other words, recoverToExpectionIf is to intercept as recovertToSucceededIf is to assertThrows. The first one allows you to perform further assertions on the expected exception. The second one gives you a result type that will satisfy the type checker at the end of the test body. Here's an example showing recoverToExceptionIf in the REPL:

scala> val futureEx =
     |   recoverToExceptionIf[IllegalStateException] {
     |     Future { throw new IllegalStateException("hello") }
     |   }
futureEx: scala.concurrent.Future[IllegalStateException] = ...

scala> futureEx.value
res6: Option[scala.util.Try[IllegalStateException]] =
    Some(Success(java.lang.IllegalStateException: hello))

scala> futureEx map { ex => assert(ex.getMessage == "world") }
res7: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res7.value
res8: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: "[hello]" did not equal "[world]"))

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, AsyncFeatureSpec provides registration methods that start with ignore instead of scenario. Here's an example:

package org.scalatest.examples.asyncfeaturespec.ignore

import org.scalatest.AsyncFeatureSpec
import scala.concurrent.Future

class AddSpec extends AsyncFeatureSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }
  def addNow(addends: Int*): Int = addends.sum

  feature("The add methods") {

    ignore("addSoon will eventually compute a sum of passed Ints") {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }

    scenario("addNow will immediately compute a sum of passed Ints") {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

If you run class AddSpec with:

scala> org.scalatest.run(new AddSpec)

It will run only the second test and report that the first test was ignored:

AddSpec:
Feature: The add methods
- Scenario: addSoon will eventually compute a sum of passed Ints !!! IGNORED !!!
- Scenario: addNow will immediately compute a sum of passed Ints

If you wish to temporarily ignore an entire suite of tests, you can (on the JVM, not Scala.js) annotate the test class with @Ignore, like this:

package org.scalatest.examples.asyncfeaturespec.ignoreall

import org.scalatest.AsyncFeatureSpec
import scala.concurrent.Future
import org.scalatest.Ignore

@Ignore
class AddSpec extends AsyncFeatureSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }
  def addNow(addends: Int*): Int = addends.sum

  feature("The add methods") {

    scenario("addSoon will eventually compute a sum of passed Ints") {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }

    scenario("addNow will immediately compute a sum of passed Ints") {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the AddSpec in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above AddSpec in the Scala interpreter, you'll see:

AddSpec:
Feature: The add methods
- Scenario: addSoon will eventually compute a sum of passed Ints !!! IGNORED !!!
- Scenario: addNow will immediately compute a sum of passed Ints !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class visible, to encourage the developers to eventually fix and “un-ignore” it. If you want to prevent a class from being discovered at all (on the JVM, not Scala.js), use the DoNotDiscover annotation instead.

If you want to ignore all tests of a suite on Scala.js, where annotations can't be inspected at runtime, you'll need to change it to ignore at each test site. To make a suite non-discoverable on Scala.js, ensure it does not declare a public no-arg constructor. You can either declare a public constructor that takes one or more arguments, or make the no-arg constructor non-public. Because this technique will also make the suite non-discoverable on the JVM, it is a good approach for suites you want to run (but not be discoverable) on both Scala.js and the JVM.

Informers

One of the parameters to AsyncFeatureSpec's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the default reporting done by AsyncFeatureSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event.

One use case for the Informer is to pass more information about a scenario to the reporter. For example, the GivenWhenThen trait provides methods that use the implicit info provided by AsyncFeatureSpec to pass such information to the reporter. You can see this in action in the initial example of this trait's documentation.

Documenters

AsyncFeatureSpec also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example FlatSpec that uses markup:

package org.scalatest.examples.asyncfeaturespec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncFeatureSpec with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

     def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  feature("An element can be added to an empty mutable Set") {
    scenario("When an element is added to an empty mutable Set") {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      markup("This test finished with a **bold** statement!")
      succeed
    }
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.asyncfeaturespec.note

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncFeatureSpec {

  feature("An element can be added to an empty mutable Set") {
    scenario("When an element is added to an empty mutable Set") {

      info("info is recorded")
      markup("markup is *also* recorded")
      note("notes are sent immediately")
      alert("alerts are also sent immediately")

      val set = mutable.Set.empty[String]
      set += "clarity"
      assert(set.size === 1)
      assert(set.contains("clarity"))
    }
  }
}

Because note and alert information is sent immediately, it will appear before the test name in string reporters, and its color will be unrelated to the ultimate outcome of the test: note text will always appear in green, alert text will always appear in yellow. Here's an example:

scala> org.scalatest.run(new SetSpec)
SetSpec:
Feature: An element can be added to an empty mutable Set
  + notes are sent immediately
  + alerts are also sent immediately
  Scenario: When an element is added to an empty mutable Set
    info is recorded
  + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality, has not yet been implemented. Here's an example:

package org.scalatest.examples.asyncfeaturespec.pending

import org.scalatest.AsyncFeatureSpec
import scala.concurrent.Future

class AddSpec extends AsyncFeatureSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }
  def addNow(addends: Int*): Int = addends.sum

  feature("The add methods") {

    scenario("addSoon will eventually compute a sum of passed Ints") (pending)

    scenario("addNow will immediately compute a sum of passed Ints") {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

(Note: "(pending)" is the body of the test. Thus the test contains just one statement, an invocation of the pending method, which throws TestPendingException.) If you run this version of AddSpec with:

scala> org.scalatest.run(new AddSpec)

It will run both tests, but report that first test is pending. You'll see:

AddSpec:
Feature: The add methods
- Scenario: addSoon will eventually compute a sum of passed Ints (pending)
- Scenario: addNow will immediately compute a sum of passed Ints

One difference between an ignored test and a pending one is that an ignored test is intended to be used during significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException.

Tagging tests

An AsyncFeatureSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing an AsyncFeatureSpec, groups of tests can optionally be included and/or excluded. To tag an AsyncFeatureSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for AsyncFeatureSpecs like this:

package org.scalatest.examples.asyncfeaturespec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place AsyncFeatureSpec tests into groups with tags like this:

import org.scalatest.AsyncFeatureSpec
import org.scalatest.tagobjects.Slow
import scala.concurrent.Future

class AddSpec extends AsyncFeatureSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }
  def addNow(addends: Int*): Int = addends.sum

  feature("The add methods") {

    scenario("addSoon will eventually compute a sum of passed Ints",
         Slow) {

      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }

    scenario("addNow will immediately compute a sum of passed Ints",
        Slow, DbTest) {

      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of an AsyncFeatureSpec in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication in async styles:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and eliminate the need to synchronize access to shared mutable state on the JVM.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgAsyncTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgAsyncTest)` instead)
`withFixture(OneArgAsyncTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or a holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.asyncfeaturespec.getfixture

import org.scalatest.AsyncFeatureSpec
import scala.concurrent.Future

class ExampleSpec extends AsyncFeatureSpec {

  def fixture: Future[String] = Future { "ScalaTest is designed to " }

  feature("Simplicity") {
    scenario("User needs to read test code written by others") {
      val future = fixture
      val result = future map { s => s + "encourage clear code!" }
      result map { s =>
        assert(s == "ScalaTest is designed to encourage clear code!")
      }
    }

    scenario("User needs to understand what the tests are doing") {
      val future = fixture
      val result = future map { s => s + "be easy to reason about!" }
      result map { s =>
        assert(s == "ScalaTest is designed to be easy to reason about!")
      }
    }
  }
}

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, you could pass in an initial value for a fixture object as a parameter to the get-fixture method.

Overriding `withFixture(NoArgAsyncTest)`

Although the get-fixture method approach takes care of setting up a fixture at the beginning of each test, it doesn't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgAsyncTest), a method defined in trait AsyncTestSuite, a supertrait of AsyncFeatureSpec.

Trait AsyncFeatureSpec's runTest method passes a no-arg async test function to withFixture(NoArgAsyncTest). It is withFixture's responsibility to invoke that test function. The default implementation of withFixture simply invokes the function and returns the result, like this:

// Default implementation in trait AsyncTestSuite
protected def withFixture(test: NoArgAsyncTest): FutureOutcome = {
  test()
}

You can, therefore, override withFixture to perform setup before invoking the test function, and/or perform cleanup after the test completes. The recommended way to ensure cleanup is performed after a test completes is to use the complete-lastly syntax, defined in supertrait CompleteLastly. The complete-lastly syntax will ensure that cleanup will occur whether future-producing code completes abruptly by throwing an exception, or returns normally yielding a future. In the latter case, complete-lastly will register the cleanup code to execute asynchronously when the future completes.

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. In other words, instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgTest) = {

  // Perform setup here

  complete {
    super.withFixture(test) // Invoke the test function
  } lastly {
    // Perform cleanup here
  }
}

If you have no cleanup to perform, you can write withFixture like this instead:

// Your implementation
override def withFixture(test: NoArgTest) = {

  // Perform setup here

  super.withFixture(test) // Invoke the test function
}

If you want to perform an action only for certain outcomes, you'll need to register code performing that action as a callback on the Future using one of Future's registration methods: onComplete, onSuccess, or onFailure. Note that if a test fails, that will be treated as a scala.util.Success(org.scalatest.Failed). So if you want to perform an action if a test fails, for example, you'd register the callback using onSuccess.

Here's an example in which withFixture(NoArgAsyncTest) is used to take a snapshot of the working directory if a test fails, and send that information to the standard output stream:

package org.scalatest.examples.asyncfeaturespec.noargasynctest

import java.io.File
import org.scalatest._
import scala.concurrent.Future

class ExampleSpec extends AsyncFeatureSpec {

  override def withFixture(test: NoArgAsyncTest) = {

    super.withFixture(test) onFailedThen { _ =>
      val currDir = new File(".")
      val fileNames = currDir.list()
      info("Dir snapshot: " + fileNames.mkString(", "))
    }
  }

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  feature("addSoon") {
    scenario("succeed case") {
      addSoon(1, 1) map { sum => assert(sum == 2) }
    }

    scenario("fail case") {
      addSoon(1, 1) map { sum => assert(sum == 3) }
    }
  }
}

Running this version of ExampleSpec in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSpec)
ExampleSpec:
Feature: addSoon
- Scenario: succeed case
- Scenario: fail case *** FAILED ***
  2 did not equal 3 (:33)

Note that the NoArgAsyncTest passed to withFixture, in addition to an apply method that executes the test, also includes the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Lastly, if you want to transform the outcome in some way in withFixture, you'll need to use either the map or transform methods of Future, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  val futureOutcome = super.withFixture(test) // Invoke the test function

  futureOutcome change { outcome =>
    // transform the outcome into a new outcome here
  }
}

Note that a NoArgAsyncTest's apply method will return a scala.util.Failure only if the test completes abruptly with a "test-fatal" exception (such as OutOfMemoryError) that should cause the suite to abort rather than the test to fail. Thus usually you would use map to transform future outcomes, not transform, so that such test-fatal exceptions pass through unchanged. The suite will abort asynchronously with any exception returned from NoArgAsyncTest's apply method in a scala.util.Failure.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

package org.scalatest.examples.asyncfeaturespec.loanfixture

import java.util.concurrent.ConcurrentHashMap

import scala.concurrent.Future
import scala.concurrent.ExecutionContext

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private final val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer // java.lang.StringBuffer is thread-safe
    databases.put(name, db)
    db
  }
  def removeDb(name: String): Unit = {
    databases.remove(name)
  }
}

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

import org.scalatest._
import DbServer._
import java.util.UUID.randomUUID

class ExampleSpec extends AsyncFeatureSpec {

  def withDatabase(testCode: Future[Db] => Future[Assertion]) = {
    val dbName = randomUUID.toString // generate a unique db name
    val futureDb = Future { createDb(dbName) } // create the fixture
    complete {
      val futurePopulatedDb =
        futureDb map { db =>
          db.append("ScalaTest is designed to ") // perform setup
        }
      testCode(futurePopulatedDb) // "loan" the fixture to the test code
    } lastly {
      removeDb(dbName) // ensure the fixture will be cleaned up
    }
  }

  def withActor(testCode: StringActor => Future[Assertion]) = {
    val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is designed to ") // set up the fixture
      testCode(actor) // "loan" the fixture to the test code
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  feature("Simplicity") {
    // This test needs the actor fixture
    scenario("User needs to read test code written by others") {
      withActor { actor =>
        actor ! Append("encourage clear code!")
        val futureString = actor ? GetValue
        futureString map { s =>
          assert(s === "ScalaTest is designed to encourage clear code!")
        }
      }
    }
    // This test needs the database fixture
    scenario("User needs to understand what the tests are doing") {
      withDatabase { futureDb =>
        futureDb map { db =>
          db.append("be easy to reason about!")
          assert(db.toString === "ScalaTest is designed to be easy to reason about!")
        }
      }
    }
    // This test needs both the actor and the database
    scenario("User needs to write tests") {
      withDatabase { futureDb =>
        withActor { actor => // loan-fixture methods compose
          actor ! Append("be easy to remember how to write!")
          val futureString = actor ? GetValue
          val futurePair: Future[(Db, String)] =
            futureDb zip futureString
          futurePair map { case (db, s) =>
            db.append("be easy to learn!")
            assert(db.toString === "ScalaTest is designed to be easy to learn!")
            assert(s === "ScalaTest is designed to be easy to remember how to write!")
          }
        }
      }
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating databases, it is a good idea to give each database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.AsyncTestSuite and overriding withFixture(OneArgAsyncTest). Each test in a fixture.AsyncTestSuite takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgAsyncTest. This withFixture method is responsible for invoking the one-arg async test function, so you can perform fixture set up before invoking and passing the fixture into the test function, and ensure clean up is performed after the test completes.

To enable the stacking of traits that define withFixture(NoArgAsyncTest), it is a good idea to let withFixture(NoArgAsyncTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgAsyncTest to a NoArgAsyncTest. You can do that by passing the fixture object to the toNoArgAsyncTest method of OneArgAsyncTest. In other words, instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgAsyncTest) method of the same instance by writing:

withFixture(test.toNoArgAsyncTest(theFixture))

Here's a complete example:

package org.scalatest.examples.asyncfeaturespec.oneargasynctest

import org.scalatest._
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSpec extends fixture.AsyncFeatureSpec {

  type FixtureParam = StringActor

  def withFixture(test: OneArgAsyncTest): FutureOutcome = {

    val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is designed to ") // set up the fixture
      withFixture(test.toNoArgAsyncTest(actor))
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  feature("Simplicity") {
    scenario("User needs to read test code written by others") { actor =>
      actor ! Append("encourage clear code!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s === "ScalaTest is designed to encourage clear code!")
      }
    }

    scenario("User needs to understand what the tests are doing") { actor =>
      actor ! Append("be easy to reason about!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s === "ScalaTest is designed to be easy to reason about!")
      }
    }
  }
}

In this example, the tests required one fixture object, a StringActor. If your tests need multiple fixture objects, you can simply define the FixtureParam type to be a tuple containing the objects or, alternatively, a case class containing the objects. For more information on the withFixture(OneArgAsyncTest) technique, see the documentation for fixture.AsyncFeatureSpec.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.asyncfeaturespec.beforeandafter

import org.scalatest.AsyncFeatureSpec
import org.scalatest.BeforeAndAfter
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSpec extends AsyncFeatureSpec with BeforeAndAfter {

  final val actor = new StringActor

  before {
    actor ! Append("ScalaTest is designed to ") // set up the fixture
  }

  after {
    actor ! Clear // clean up the fixture
  }

  feature("Simplicity") {
    scenario("User needs to read test code written by others") {
      actor ! Append("encourage clear code!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is designed to encourage clear code!")
      }
    }

    scenario("User needs to understand what the tests are doing") {
      actor ! Append("be easy to reason about!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is designed to be easy to reason about!")
      }
    }
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state.

Note that on the JVM, if you override ScalaTest's default serial execution context, you will likely need to worry about synchronizing access to shared mutable fixture state, because the execution context may assign different threads to process different Future transformations. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, it can be difficult to spot cases where these constraints are violated. The best approach is to use only immutable objects when transforming Futures. When that's not practical, involve only thread-safe mutable objects, as is done in the above example. On Scala.js, by contrast, you need not worry about thread synchronization, because in effect only one thread exists.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilderActor and StringBufferActor fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.asyncfeaturespec.composingwithasyncfixture

import org.scalatest._
import org.scalatest.SuiteMixin
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val builderActor = new StringBuilderActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    builderActor ! Append("ScalaTest is designed to ")
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      builderActor ! Clear
    }
  }
}

trait Buffer extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val bufferActor = new StringBufferActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      bufferActor ! Clear
    }
  }
}

class ExampleSpec extends AsyncFeatureSpec with Builder with Buffer {

  feature("Simplicity") {
    scenario("User needs to read test code written by others") {
      builderActor ! Append("encourage clear code!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is designed to encourage clear code!")
        assert(lst.isEmpty)
        bufferActor ! Append("sweet")
        succeed
      }
    }

    scenario("User needs to understand what the tests are doing") {
      builderActor ! Append("be easy to reason about!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is designed to be easy to reason about!")
        assert(lst.isEmpty)
        bufferActor ! Append("awesome")
        succeed
      }
    }
  }
}

By mixing in both the Builder and Buffer traits, ExampleSpec gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Spec extends AsyncFeatureSpec with Buffer with Builder

If you only need one fixture you mix in only that trait:

class Example3Spec extends AsyncFeatureSpec with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.asyncfeaturespec.composingbeforeandaftereach

import org.scalatest._
import org.scalatest.BeforeAndAfterEach
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends BeforeAndAfterEach { this: Suite =>

  final val builderActor = new StringBuilderActor

  override def beforeEach() {
    builderActor ! Append("ScalaTest is designed to ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builderActor ! Clear
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  final val bufferActor = new StringBufferActor

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally bufferActor ! Clear
  }
}

class ExampleSpec extends AsyncFeatureSpec with Builder with Buffer {

  feature("Simplicity") {

    scenario("User needs to read test code written by others") {
      builderActor ! Append("encourage clear code!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is designed to encourage clear code!")
        assert(lst.isEmpty)
        bufferActor ! Append("sweet")
        succeed
      }
    }

    scenario("User needs to understand what the tests are doing") {
      builderActor ! Append("be easy to reason about!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is designed to be easy to reason about!")
        assert(lst.isEmpty)
        bufferActor ! Append("awesome")
        succeed
      }
    }
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in an AsyncFeatureSpec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any AsyncFeatureSpec that uses them, so that the tests they contain will be registered as tests in that AsyncFeatureSpec. For example, given this StackActor class:

package org.scalatest.examples.asyncfeaturespec.sharedtests

import scala.collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Stack operations
case class Push[T](value: T)
sealed abstract class StackOp
case object Pop extends StackOp
case object Peek extends StackOp
case object Size extends StackOp

// Stack info
case class StackInfo[T](top: Option[T], size: Int, max: Int) {
  require(size >= 0, "size was less than zero")
  require(max >= size, "max was less than size")
  val isFull: Boolean = size == max
  val isEmpty: Boolean = size == 0
}

class StackActor[T](Max: Int, name: String) {

  private final val buf = new ListBuffer[T]

  def !(push: Push[T]): Unit =
    synchronized {
      if (buf.size != Max)
        buf.prepend(push.value)
      else
        throw new IllegalStateException("can't push onto a full stack")
    }

  def ?(op: StackOp)(implicit c: ExecutionContext): Future[StackInfo[T]] =
    synchronized {
      op match {
        case Pop =>
          Future {
            if (buf.size != 0)
              StackInfo(Some(buf.remove(0)), buf.size, Max)
            else
              throw new IllegalStateException("can't pop an empty stack")
          }
        case Peek =>
          Future {
            if (buf.size != 0)
              StackInfo(Some(buf(0)), buf.size, Max)
            else
              throw new IllegalStateException("can't peek an empty stack")
          }
        case Size =>
          Future { StackInfo(None, buf.size, Max) }
      }
    }

  override def toString: String = name
}

You may want to test the stack represented by the StackActor class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several tests that make sense any time the stack is non-empty. Thus you'd ideally want to run those same tests for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these tests out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your AsyncFeatureSpec for StackActor, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared tests are run for all three fixtures.

You can define a behavior function that encapsulates these shared tests inside the AsyncFeatureSpec that uses them. If they are shared between different AsyncFeatureSpecs, however, you could also define them in a separate trait that is mixed into each AsyncFeatureSpec that uses them. For example, here the nonEmptyStackActor behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared tests for non-full stacks:

import org.scalatest.AsyncFeatureSpec

trait AsyncFeatureSpecStackBehaviors { this: AsyncFeatureSpec =>

  def nonEmptyStackActor(createNonEmptyStackActor: => StackActor[Int],
        lastItemAdded: Int, name: String): Unit = {

    scenario("Size is fired at non-empty stack actor: " + name) {
      val stackActor = createNonEmptyStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isEmpty)
      }
    }

    scenario("Peek is fired at non-empty stack actor: " + name) {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePeek <- stackActor ? Size
          afterPeek <- stackActor ? Peek
        } yield (beforePeek, afterPeek)
      futurePair map { case (beforePeek, afterPeek) =>
        assert(afterPeek.top == Some(lastItemAdded))
        assert(afterPeek.size == beforePeek.size)
      }
    }

    scenario("Pop is fired at non-empty stack actor: " + name) {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePop <- stackActor ? Size
          afterPop <- stackActor ? Pop
        } yield (beforePop, afterPop)
      futurePair map { case (beforePop, afterPop) =>
        assert(afterPop.top == Some(lastItemAdded))
        assert(afterPop.size == beforePop.size - 1)
      }
    }
  }

  def nonFullStackActor(createNonFullStackActor: => StackActor[Int], name: String): Unit = {

    scenario("Size is fired at non-full stack actor: " + name) {
      val stackActor = createNonFullStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isFull)
      }
    }

    scenario("Push is fired at non-full stack actor: " + name) {
      val stackActor = createNonFullStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePush <- stackActor ? Size
          afterPush <- { stackActor ! Push(7); stackActor ? Peek }
        } yield (beforePush, afterPush)
      futurePair map { case (beforePush, afterPush) =>
        assert(afterPush.size == beforePush.size + 1)
        assert(afterPush.top == Some(7))
      }
    }
  }
}

Given these behavior functions, you could invoke them directly, but AsyncFeatureSpec offers a DSL for the purpose, which looks like this:

scenariosFor(nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName))
scenariosFor(nonFullStackActor(almostEmptyStackActor, almostEmptyStackActorName))

Here's an example:

class StackSpec extends AsyncFeatureSpec with AsyncFeatureSpecStackBehaviors {

  val Max = 10
  val LastValuePushed = Max - 1

  // Stack fixture creation methods
  val emptyStackActorName = "empty stack actor"
  def emptyStackActor = new StackActor[Int](Max, emptyStackActorName )

  val fullStackActorName = "full stack actor"
  def fullStackActor = {
    val stackActor = new StackActor[Int](Max, fullStackActorName )
    for (i <- 0 until Max)
      stackActor ! Push(i)
    stackActor
  }

  val almostEmptyStackActorName = "almost empty stack actor"
  def almostEmptyStackActor = {
    val stackActor = new StackActor[Int](Max, almostEmptyStackActorName )
    stackActor ! Push(LastValuePushed)
    stackActor
  }

  val almostFullStackActorName = "almost full stack actor"
  def almostFullStackActor = {
    val stackActor = new StackActor[Int](Max, almostFullStackActorName)
    for (i <- 1 to LastValuePushed)
      stackActor ! Push(i)
    stackActor
  }

  feature("A Stack is pushed and popped") {

    scenario("Size is fired at empty stack actor") {
      val stackActor = emptyStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(stackInfo.isEmpty)
      }
    }

    scenario("Peek is fired at empty stack actor") {
      recoverToSucceededIf[IllegalStateException] {
        emptyStackActor ? Peek
      }
    }

    scenario("Pop is fired at empty stack actor") {
      recoverToSucceededIf[IllegalStateException] {
        emptyStackActor ? Pop
      }
    }

    scenariosFor(nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName))
    scenariosFor(nonFullStackActor(almostEmptyStackActor, almostEmptyStackActorName))

    scenariosFor(nonEmptyStackActor(almostFullStackActor, LastValuePushed, almostFullStackActorName))
    scenariosFor(nonFullStackActor(almostFullStackActor, almostFullStackActorName))

    scenario("full is invoked on a full stack") {
      val stackActor = fullStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(stackInfo.isFull)
      }
    }

    scenariosFor(nonEmptyStackActor(fullStackActor, LastValuePushed, fullStackActorName))

    scenario("push is invoked on a full stack") {
      val stackActor = fullStackActor
      assertThrows[IllegalStateException] {
        stackActor ! Push(10)
      }
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> org.scalatest.run(new StackSpec)
StackSpec:
Feature: A Stack actor
- Scenario: Size is fired at empty stack actor
- Scenario: Peek is fired at empty stack actor
- Scenario: Pop is fired at empty stack actor
- Scenario: Size is fired at non-empty stack actor: almost empty stack actor
- Scenario: Peek is fired at non-empty stack actor: almost empty stack actor
- Scenario: Pop is fired at non-empty stack actor: almost empty stack actor
- Scenario: Size is fired at non-full stack actor: almost empty stack actor
- Scenario: Push is fired at non-full stack actor: almost empty stack actor
- Scenario: Size is fired at non-empty stack actor: almost full stack actor
- Scenario: Peek is fired at non-empty stack actor: almost full stack actor
- Scenario: Pop is fired at non-empty stack actor: almost full stack actor
- Scenario: Size is fired at non-full stack actor: almost full stack actor
- Scenario: Push is fired at non-full stack actor: almost full stack actor
- Scenario: Size is fired at full stack actor
- Scenario: Size is fired at non-empty stack actor: full stack actor
- Scenario: Peek is fired at non-empty stack actor: full stack actor
- Scenario: Pop is fired at non-empty stack actor: full stack actor
- Scenario: Push is fired at full stack actor

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. Although in an AsyncFeatureSpec, the feature clause is a nesting construct analogous to AsyncFunSpec's describe clause, you many sometimes need to do a bit of extra work to ensure that the test names are unique. If a duplicate test name problem shows up in an AsyncFeatureSpec, you'll need to pass in a prefix or suffix string to add to each test name. You can call toString on the shared fixture object, or pass this string the same way you pass any other data needed by the shared tests. This is the approach taken by the previous AsyncFeatureSpecStackBehaviors example.

Given this AsyncFeatureSpecStackBehaviors trait, calling it with the almostEmptyStackActor fixture, like this:

scenariosFor(nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName))

yields test names:

Size is fired at non-empty stack actor: almost empty stack actor
Peek is fired at non-empty stack actor: almost empty stack actor
Pop is fired at non-empty stack actor: almost empty stack actor

Whereas calling it with the almostFullStackActor fixture, like this:

scenariosFor(nonEmptyStack(almostFullStackActor, lastValuePushed, almostFullStackActorName))

yields different test names:

Size is fired at non-empty stack actor: almost full stack actor
Peek is fired at non-empty stack actor: almost full stack actor
Pop is fired at non-empty stack actor: almost full stack actor

trait AsyncFeatureSpecLike extends AsyncTestSuite with AsyncTestRegistration with Informing with Notifying with Alerting with Documenting

Implementation trait for class AsyncFeatureSpec, which represents a suite of tests in which each test represents one scenario of a feature.

AsyncFeatureSpec is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of AsyncFeatureSpec into some other class, you can use this trait instead, because class AsyncFeatureSpec does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of AsyncFeatureSpec.

abstract class AsyncFlatSpec extends AsyncFlatSpecLike

Enables testing of asynchronous code without blocking, using a style consistent with traditional FlatSpec tests.

Recommended Usage: AsyncFlatSpec is intended to enable users of FlatSpec to write non-blocking asynchronous tests that are consistent with their traditional FlatSpec tests. Note: AsyncFlatSpec is intended for use in special situations where non-blocking asynchronous testing is needed, with class FlatSpec used for general needs.

Given a Future returned by the code you are testing, you need not block until the Future completes before performing assertions against its value. You can instead map those assertions onto the Future and return the resulting Future[Assertion] to ScalaTest. The test will complete asynchronously, when the Future[Assertion] completes.

Trait AsyncFlatSpec is so named because your specification text and tests line up flat against the left-side indentation level, with no nesting needed. Here's an example AsyncFlatSpec:

package org.scalatest.examples.asyncflatspec

import org.scalatest.AsyncFlatSpec
import scala.concurrent.Future

class AddSpec extends AsyncFlatSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  behavior of "addSoon"

  it should "eventually compute a sum of passed Ints" in {
    val futureSum: Future[Int] = addSoon(1, 2)
    // You can map assertions onto a Future, then return
    // the resulting Future[Assertion] to ScalaTest:
    futureSum map { sum => assert(sum == 3) }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" should "immediately compute a sum of passed Ints" in {
    val sum: Int = addNow(1, 2)
    // You can also write synchronous tests. The body
    // must have result type Assertion:
    assert(sum == 3)
  }
}

The initial test in this example demonstrates the use of an explicit behavior of clause, which establishes addSoon as the subject. The second test demonstrates the alternate syntax of replacing the first it with the subject string, in this case, "addNow". As with traditional FlatSpecs, you can use must or can as well as should. For example, instead of it should "eventually..., you could write it must "eventually... or it can "eventually.... You can also write they instead of it. See the documentation for FlatSpec for more detail.

Running the above AddSpec in the Scala interpreter would yield:

addSoon
- should eventually compute a sum of passed Ints
- should immediately compute a sum of passed Ints

Starting with version 3.0.0, ScalaTest assertions and matchers have result type Assertion. The result type of the first test in the example above, therefore, is Future[Assertion]. For clarity, here's the relevant code in a REPL session:

scala> import org.scalatest._
import org.scalatest._

scala> import Assertions._
import Assertions._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext
import scala.concurrent.ExecutionContext

scala> implicit val executionContext = ExecutionContext.Implicits.global
executionContext: scala.concurrent.ExecutionContextExecutor = scala.concurrent.impl.ExecutionContextImpl@26141c5b

scala> def addSoon(addends: Int*): Future[Int] = Future { addends.sum }
addSoon: (addends: Int*)scala.concurrent.Future[Int]

scala> val futureSum: Future[Int] = addSoon(1, 2)
futureSum: scala.concurrent.Future[Int] = scala.concurrent.impl.Promise$DefaultPromise@721f47b2

scala> futureSum map { sum => assert(sum == 3) }
res0: scala.concurrent.Future[org.scalatest.Assertion] = scala.concurrent.impl.Promise$DefaultPromise@3955cfcb

The second test has result type Assertion:

scala> def addNow(addends: Int*): Int = addends.sum
addNow: (addends: Int*)Int

scala> val sum: Int = addNow(1, 2)
sum: Int = 3

scala> assert(sum == 3)
res1: org.scalatest.Assertion = Succeeded

When AddSpec is constructed, the second test will be implicitly converted to Future[Assertion] and registered. The implicit conversion is from Assertion to Future[Assertion], so you must end synchronous tests in some ScalaTest assertion or matcher expression. If a test would not otherwise end in type Assertion, you can place succeed at the end of the test. succeed, a field in trait Assertions, returns the Succeeded singleton:

scala> succeed
res2: org.scalatest.Assertion = Succeeded

Thus placing succeed at the end of a test body will satisfy the type checker:

"addNow" should "immediately compute a sum of passed Ints" in {
  val sum: Int = addNow(1, 2)
  assert(sum == 3)
  println("hi") // println has result type Unit
  succeed       // succeed has result type Assertion
}

An AsyncFlatSpec's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Tests can only be registered with the it method while the AsyncFlatSpec is in its registration phase. Any attempt to register a test after the AsyncFlatSpec has entered its ready phase, i.e., after run has been invoked on the AsyncFlatSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using AsyncFlatSpec is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Asynchronous execution model

AsyncFlatSpec extends AsyncTestSuite, which provides an implicit scala.concurrent.ExecutionContext named executionContext. This execution context is used by AsyncFlatSpec to transform the Future[Assertion]s returned by each test into the FutureOutcome returned by the test function passed to withFixture. This ExecutionContext is also intended to be used in the tests, including when you map assertions onto futures.

On both the JVM and Scala.js, the default execution context provided by ScalaTest's asynchronous testing styles confines execution to a single thread per test. On JavaScript, where single-threaded execution is the only possibility, the default execution context is scala.scalajs.concurrent.JSExecutionContext.Implicits.queue. On the JVM, the default execution context is a serial execution context provided by ScalaTest itself.

When ScalaTest's serial execution context is called upon to execute a task, that task is recorded in a queue for later execution. For example, one task that will be placed in this queue is the task that transforms the Future[Assertion] returned by an asynchronous test body to the FutureOutcome returned from the test function. Other tasks that will be queued are any transformations of, or callbacks registered on, Futures that occur in your test body, including any assertions you map onto Futures. Once the test body returns, the thread that executed the test body will execute the tasks in that queue one after another, in the order they were enqueued.

ScalaTest provides its serial execution context as the default on the JVM for three reasons. First, most often running both tests and suites in parallel does not give a significant performance boost compared to just running suites in parallel. Thus parallel execution of Future transformations within individual tests is not generally needed for performance reasons.

Second, if multiple threads are operating in the same suite concurrently, you'll need to make sure access to any mutable fixture objects by multiple threads is synchronized. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, this does not hold true for callbacks, and in general it is easy to make a mistake. Simply put: synchronizing access to shared mutable state is difficult and error prone. Because ScalaTest's default execution context on the JVM confines execution of Future transformations and call backs to a single thread, you need not (by default) worry about synchronizing access to mutable state in your asynchronous-style tests.

Third, asynchronous-style tests need not be complete when the test body returns, because the test body returns a Future[Assertion]. This Future[Assertion] will often represent a test that has not yet completed. As a result, when using a more traditional execution context backed by a thread-pool, you could potentially start many more tests executing concurrently than there are threads in the thread pool. The more concurrently execute tests you have competing for threads from the same limited thread pool, the more likely it will be that tests will intermitently fail due to timeouts.

Using ScalaTest's serial execution context on the JVM will ensure the same thread that produced the Future[Assertion] returned from a test body is also used to execute any tasks given to the execution context while executing the test body—and that thread will not be allowed to do anything else until the test completes. If the serial execution context's task queue ever becomes empty while the Future[Assertion] returned by that test's body has not yet completed, the thread will block until another task for that test is enqueued. Although it may seem counter-intuitive, this blocking behavior means the total number of tests allowed to run concurrently will be limited to the total number of threads executing suites. This fact means you can tune the thread pool such that maximum performance is reached while avoiding (or at least, reducing the likelihood of) tests that fail due to timeouts because of thread competition.

This thread confinement strategy does mean, however, that when you are using the default execution context on the JVM, you must be sure to never block in the test body waiting for a task to be completed by the execution context. If you block, your test will never complete. This kind of problem will be obvious, because the test will consistently hang every time you run it. (If a test is hanging, and you're not sure which one it is, enable slowpoke notifications.) If you really do want to block in your tests, you may wish to just use a traditional FlatSpec with ScalaFutures instead. Alternatively, you could override the executionContext and use a traditional ExecutionContext backed by a thread pool. This will enable you to block in an asynchronous-style test on the JVM, but you'll need to worry about synchronizing access to shared mutable state.

To use a different execution context, just override executionContext. For example, if you prefer to use the runNow execution context on Scala.js instead of the default queue, you would write:

// on Scala.js
implicit override def executionContext =
    scala.scalajs.concurrent.JSExecutionContext.Implicits.runNow

If you prefer on the JVM to use the global execution context, which is backed by a thread pool, instead of ScalaTest's default serial execution contex, which confines execution to a single thread, you would write:

// on the JVM (and also compiles on Scala.js, giving
// you the queue execution context)
implicit override def executionContext =
    scala.concurrent.ExecutionContext.Implicits.global

Serial and parallel test execution

By default (unless you mix in ParallelTestExecution), tests in an AsyncFlatSpec will be executed one after another, i.e., serially. This is true whether those tests return Assertion or Future[Assertion], no matter what threads are involved. This default behavior allows you to re-use a shared fixture, such as an external database that needs to be cleaned after each test, in multiple tests in async-style suites. This is implemented by registering each test, other than the first test, to run as a continuation after the previous test completes.

If you want the tests of an AsyncFlatSpec to be executed in parallel, you must mix in ParallelTestExecution and enable parallel execution of tests in your build. You enable parallel execution in Runner with the -P command line flag. In the ScalaTest Maven Plugin, set parallel to true. In sbt, parallel execution is the default, but to be explicit you can write:

parallelExecution in Test := true // the default in sbt

On the JVM, if both ParallelTestExecution is mixed in and parallel execution is enabled in the build, tests in an async-style suite will be started in parallel, using threads from the Distributor, and allowed to complete in parallel, using threads from the executionContext. If you are using ScalaTest's serial execution context, the JVM default, asynchronous tests will run in parallel very much like traditional (such as FlatSpec) tests run in parallel: 1) Because ParallelTestExecution extends OneInstancePerTest, each test will run in its own instance of the test class, you need not worry about synchronizing access to mutable instance state shared by different tests in the same suite. 2) Because the serial execution context will confine the execution of each test to the single thread that executes the test body, you need not worry about synchronizing access to shared mutable state accessed by transformations and callbacks of Futures inside the test.

If ParallelTestExecution is mixed in but parallel execution of suites is not enabled, asynchronous tests on the JVM will be started sequentially, by the single thread that invoked run, but without waiting for one test to complete before the next test is started. As a result, asynchronous tests will be allowed to complete in parallel, using threads from the executionContext. If you are using the serial execution context, however, you'll see the same behavior you see when parallel execution is disabled and a traditional suite that mixes in ParallelTestExecution is executed: the tests will run sequentially. If you use an execution context backed by a thread-pool, such as global, however, even though tests will be started sequentially by one thread, they will be allowed to run concurrently using threads from the execution context's thread pool.

The latter behavior is essentially what you'll see on Scala.js when you execute a suite that mixes in ParallelTestExecution. Because only one thread exists when running under JavaScript, you can't "enable parallel execution of suites." However, it may still be useful to run tests in parallel on Scala.js, because tests can invoke API calls that are truly asynchronous by calling into external APIs that take advantage of non-JavaScript threads. Thus on Scala.js, ParallelTestExecution allows asynchronous tests to run in parallel, even though they must be started sequentially. This may give you better performance when you are using API calls in your Scala.js tests that are truly asynchronous.

Futures and expected exceptions

If you need to test for expected exceptions in the context of futures, you can use the recoverToSucceededIf and recoverToExceptionIf methods of trait RecoverMethods. Because this trait is mixed into supertrait AsyncTestSuite, both of these methods are available by default in an AsyncFlatSpec.

If you just want to ensure that a future fails with a particular exception type, and do not need to inspect the exception further, use recoverToSucceededIf:

recoverToSucceededIf[IllegalStateException] { // Result type: Future[Assertion]
  emptyStackActor ? Peek
}

The recoverToSucceededIf method performs a job similar to assertThrows, except in the context of a future. It transforms a Future of any type into a Future[Assertion] that succeeds only if the original future fails with the specified exception. Here's an example in the REPL:

scala> import org.scalatest.RecoverMethods._
import org.scalatest.RecoverMethods._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.ExecutionContext.Implicits.global

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new IllegalStateException }
     | }
res0: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res0.value
res1: Option[scala.util.Try[org.scalatest.Assertion]] = Some(Success(Succeeded))

Otherwise it fails with an error message similar to those given by assertThrows:

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new RuntimeException }
     | }
res2: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res2.value
res3: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but java.lang.RuntimeException
      was thrown))

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { 42 }
     | }
res4: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res4.value
res5: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but no exception was thrown))

The recoverToExceptionIf method differs from the recoverToSucceededIf in its behavior when the assertion succeeds: recoverToSucceededIf yields a Future[Assertion], whereas recoverToExceptionIf yields a Future[T], where T is the expected exception type.

recoverToExceptionIf[IllegalStateException] { // Result type: Future[IllegalStateException]
  emptyStackActor ? Peek
}

In other words, recoverToExpectionIf is to intercept as recovertToSucceededIf is to assertThrows. The first one allows you to perform further assertions on the expected exception. The second one gives you a result type that will satisfy the type checker at the end of the test body. Here's an example showing recoverToExceptionIf in the REPL:

scala> val futureEx =
     |   recoverToExceptionIf[IllegalStateException] {
     |     Future { throw new IllegalStateException("hello") }
     |   }
futureEx: scala.concurrent.Future[IllegalStateException] = ...

scala> futureEx.value
res6: Option[scala.util.Try[IllegalStateException]] =
    Some(Success(java.lang.IllegalStateException: hello))

scala> futureEx map { ex => assert(ex.getMessage == "world") }
res7: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res7.value
res8: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: "[hello]" did not equal "[world]"))

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, AsyncFlatSpec provides two ways to ignore a test, both demonstrated in the following example:

package org.scalatest.examples.asyncflatspec.ignore

import org.scalatest.AsyncFlatSpec
import scala.concurrent.Future

class AddSpec extends AsyncFlatSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  behavior of "addSoon"

  ignore should "eventually compute a sum of passed Ints" in {
    val futureSum: Future[Int] = addSoon(1, 2)
    // You can map assertions onto a Future, then return
    // the resulting Future[Assertion] to ScalaTest:
    futureSum map { sum => assert(sum == 3) }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" should "immediately compute a sum of passed Ints" ignore {
    val sum: Int = addNow(1, 2)
    // You can also write synchronous tests. The body
    // must have result type Assertion:
    assert(sum == 3)
  }
}

In the first test, ignore is used instead of it. In the second test, which uses the shorthand notation, no it exists to change into ignore. To ignore such tests, you must instead change in to ignore, as shown in the above example. If you run this version of AddSpec with:

scala> org.scalatest.run(new AddSpec)

It will report both tests as ignored:

AddSpec:
addSoon
- should eventually compute a sum of passed Ints !!! IGNORED !!!
addNow
- should immediately compute a sum of passed Ints !!! IGNORED !!!

If you wish to temporarily ignore an entire suite of tests, you can (on the JVM, not Scala.js) annotate the test class with @Ignore, like this:

package org.scalatest.examples.asyncflatspec.ignoreall

import org.scalatest.AsyncFlatSpec
import scala.concurrent.Future
import org.scalatest.Ignore

@Ignore
class AddSpec extends AsyncFlatSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" should "eventually compute a sum of passed Ints" in {
    val futureSum: Future[Int] = addSoon(1, 2)
    // You can map assertions onto a Future, then return
    // the resulting Future[Assertion] to ScalaTest:
    futureSum map { sum => assert(sum == 3) }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" should "immediately compute a sum of passed Ints" in {
    val sum: Int = addNow(1, 2)
    // You can also write synchronous tests. The body
    // must have result type Assertion:
    assert(sum == 3)
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the AddSpec in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above AddSpec in the Scala interpreter, you'll see:

AddSpec:
addSoon
- should eventually compute a sum of passed Ints !!! IGNORED !!!
addNow
- should immediately compute a sum of passed Ints !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class visible, to encourage the developers to eventually fix and “un-ignore” it. If you want to prevent a class from being discovered at all (on the JVM, not Scala.js), use the DoNotDiscover annotation instead.

If you want to ignore all tests of a suite on Scala.js, where annotations can't be inspected at runtime, you'll need to change it to ignore at each test site. To make a suite non-discoverable on Scala.js, ensure it does not declare a public no-arg constructor. You can either declare a public constructor that takes one or more arguments, or make the no-arg constructor non-public. Because this technique will also make the suite non-discoverable on the JVM, it is a good approach for suites you want to run (but not be discoverable) on both Scala.js and the JVM.

Informers

One of the parameters to AsyncFlatSpec's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the reporting done by default by AsyncFlatSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event.

One use case for the Informer is to pass more information about a specification to the reporter. For example, the GivenWhenThen trait provides methods that use the implicit info provided by AsyncFlatSpec to pass such information to the reporter. Here's an example:

package org.scalatest.examples.asyncflatspec.info

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncFlatSpec with GivenWhenThen {

  "A mutable Set" should "allow an element to be added" in {
    Given("an empty mutable Set")
    val set = mutable.Set.empty[String]

    When("an element is added")
    set += "clarity"

    Then("the Set should have size 1")
    assert(set.size === 1)

    And("the Set should contain the added element")
    assert(set.contains("clarity"))

    info("That's all folks!")
    succeed
  }
}

If you run this AsyncFlatSpec from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSpec)
SetSpec:
A mutable Set
- should allow an element to be added
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

Documenters

AsyncFlatSpec also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example AsyncFlatSpec that uses markup:

package org.scalatest.examples.asyncflatspec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncFlatSpec with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

    def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  "A mutable Set" should "allow an element to be added" in {
    Given("an empty mutable Set")
    val set = mutable.Set.empty[String]

    When("an element is added")
    set += "clarity"

    Then("the Set should have size 1")
    assert(set.size === 1)

    And("the Set should contain the added element")
    assert(set.contains("clarity"))

    markup("This test finished with a **bold** statement!")
    succeed
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.asyncflatspec.note

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncFlatSpec {

  "A mutable Set" should "allow an element to be added" in {

    info("info is recorded")
    markup("markup is *also* recorded")
    note("notes are sent immediately")
    alert("alerts are also sent immediately")

    val set = mutable.Set.empty[String]
    set += "clarity"
    assert(set.size === 1)
    assert(set.contains("clarity"))
  }
}

Because note and alert information is sent immediately, it will appear before the test name in string reporters, and its color will be unrelated to the ultimate outcome of the test: note text will always appear in green, alert text will always appear in yellow. Here's an example:

scala> org.scalatest.run(new SetSpec)
SetSpec:
A mutable Set
  + notes are sent immediately
  + alerts are also sent immediately
- should allow an element to be added
  + info is recorded
  + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality, has not yet been implemented. Here's an example:

package org.scalatest.examples.asyncflatspec.pending

import org.scalatest.AsyncFlatSpec
import scala.concurrent.Future

class AddSpec extends AsyncFlatSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" should "eventually compute a sum of passed Ints" in (pending)

  def addNow(addends: Int*): Int = addends.sum

  "addNow" should "immediately compute a sum of passed Ints" in {
    val sum: Int = addNow(1, 2)
    // You can also write synchronous tests. The body
    // must have result type Assertion:
    assert(sum == 3)
  }
}

(Note: "(pending)" is the body of the test. Thus the test contains just one statement, an invocation of the pending method, which throws TestPendingException.) If you run this version of AddSpec with:

scala> org.scalatest.run(new AddSpec)

It will run both tests, but report that first test is pending. You'll see:

AddSpec:
addSoon
- should eventually compute a sum of passed Ints (pending)
addNow
- should immediately compute a sum of passed Ints

One difference between an ignored test and a pending one is that an ignored test is intended to be used during significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException.

Tagging tests

An AsyncFlatSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing an AsyncFlatSpec, groups of tests can optionally be included and/or excluded. To tag an AsyncFlatSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for AsyncFlatSpecs like this:

package org.scalatest.examples.asyncflatspec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place AsyncFlatSpec tests into groups with tags like this:

import org.scalatest.AsyncFlatSpec
import org.scalatest.tagobjects.Slow
import scala.concurrent.Future

class AddSpec extends AsyncFlatSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" should "eventually compute a sum of passed Ints" taggedAs(Slow) in {
    val futureSum: Future[Int] = addSoon(1, 2)
    // You can map assertions onto a Future, then return
    // the resulting Future[Assertion] to ScalaTest:
    futureSum map { sum => assert(sum == 3) }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" should "immediately compute a sum of passed Ints" taggedAs(Slow, DbTest) in {
    val sum: Int = addNow(1, 2)
    // You can also write synchronous tests. The body
    // must have result type Assertion:
    assert(sum == 3)
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of an AsyncFlatSpec in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication in async styles:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and eliminate the need to synchronize access to shared mutable state on the JVM.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgAsyncTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgAsyncTest)` instead)
`withFixture(OneArgAsyncTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or a holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.asyncflatspec.getfixture

import org.scalatest.AsyncFlatSpec
import scala.concurrent.Future

class ExampleSpec extends AsyncFlatSpec {

  def fixture: Future[String] = Future { "ScalaTest is " }

  "Testing" should "be easy" in {
    val future = fixture
    val result = future map { s => s + "easy!" }
    result map { s =>
      assert(s == "ScalaTest is easy!")
    }
  }

  it should "be fun" in {
    val future = fixture
    val result = future map { s => s + "fun!" }
    result map { s =>
      assert(s == "ScalaTest is fun!")
    }
  }
}

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, you could pass in an initial value for a fixture object as a parameter to the get-fixture method.

Overriding `withFixture(NoArgAsyncTest)`

Although the get-fixture method approach takes care of setting up a fixture at the beginning of each test, it doesn't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgAsyncTest), a method defined in trait AsyncTestSuite, a supertrait of AsyncFlatSpec.

Trait AsyncFlatSpec's runTest method passes a no-arg async test function to withFixture(NoArgAsyncTest). It is withFixture's responsibility to invoke that test function. The default implementation of withFixture simply invokes the function and returns the result, like this:

// Default implementation in trait AsyncTestSuite
protected def withFixture(test: NoArgAsyncTest): FutureOutcome = {
  test()
}

You can, therefore, override withFixture to perform setup before invoking the test function, and/or perform cleanup after the test completes. The recommended way to ensure cleanup is performed after a test completes is to use the complete-lastly syntax, defined in supertrait CompleteLastly. The complete-lastly syntax will ensure that cleanup will occur whether future-producing code completes abruptly by throwing an exception, or returns normally yielding a future. In the latter case, complete-lastly will register the cleanup code to execute asynchronously when the future completes.

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. In other words, instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  complete {
    super.withFixture(test) // Invoke the test function
  } lastly {
    // Perform cleanup here
  }
}

If you have no cleanup to perform, you can write withFixture like this instead:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  super.withFixture(test) // Invoke the test function
}

If you want to perform an action only for certain outcomes, you'll need to register code performing that action as a callback on the Future using one of Future's registration methods: onComplete, onSuccess, or onFailure. Note that if a test fails, that will be treated as a scala.util.Success(org.scalatest.Failed). So if you want to perform an action if a test fails, for example, you'd register the callback using onSuccess.

Here's an example in which withFixture(NoArgAsyncTest) is used to take a snapshot of the working directory if a test fails, and send that information to the standard output stream:

package org.scalatest.examples.asyncflatspec.noargasynctest

import java.io.File
import org.scalatest._
import scala.concurrent.Future

class ExampleSpec extends AsyncFlatSpec {

  override def withFixture(test: NoArgAsyncTest) = {

    super.withFixture(test) onFailedThen { _ =>
      val currDir = new File(".")
      val fileNames = currDir.list()
      info("Dir snapshot: " + fileNames.mkString(", "))
    }
  }

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "This test" should "succeed" in {
    addSoon(1, 1) map { sum => assert(sum == 2) }
  }

  it should "fail" in {
    addSoon(1, 1) map { sum => assert(sum == 3) }
  }
}

Running this version of ExampleSpec in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSpec)
ExampleSpec:
This test
- should succeed
- should fail *** FAILED ***
  2 did not equal 3 (:33)

Note that the NoArgAsyncTest passed to withFixture, in addition to an apply method that executes the test, also includes the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Lastly, if you want to transform the outcome in some way in withFixture, you'll need to use either the map or transform methods of Future, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  val futureOutcome = super.withFixture(test) // Invoke the test function

  futureOutcome change { outcome =>
    // transform the outcome into a new outcome here
  }
}

Note that a NoArgAsyncTest's apply method will return a scala.util.Failure only if the test completes abruptly with a "test-fatal" exception (such as OutOfMemoryError) that should cause the suite to abort rather than the test to fail. Thus usually you would use map to transform future outcomes, not transform, so that such test-fatal exceptions pass through unchanged. The suite will abort asynchronously with any exception returned from NoArgAsyncTest's apply method in a scala.util.Failure.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

package org.scalatest.examples.asyncflatspec.loanfixture

import java.util.concurrent.ConcurrentHashMap

import scala.concurrent.Future
import scala.concurrent.ExecutionContext

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private final val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer // java.lang.StringBuffer is thread-safe
    databases.put(name, db)
    db
  }
  def removeDb(name: String): Unit = {
    databases.remove(name)
  }
}

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

import org.scalatest._
import DbServer._
import java.util.UUID.randomUUID

class ExampleSpec extends AsyncFlatSpec {

  def withDatabase(testCode: Future[Db] => Future[Assertion]) = {
    val dbName = randomUUID.toString // generate a unique db name
    val futureDb = Future { createDb(dbName) } // create the fixture
    complete {
      val futurePopulatedDb =
        futureDb map { db =>
          db.append("ScalaTest is ") // perform setup
        }
      testCode(futurePopulatedDb) // "loan" the fixture to the test code
    } lastly {
      removeDb(dbName) // ensure the fixture will be cleaned up
    }
  }

  def withActor(testCode: StringActor => Future[Assertion]) = {
    val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is ") // set up the fixture
      testCode(actor) // "loan" the fixture to the test code
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  // This test needs the actor fixture
  "Testing" should "be productive" in {
    withActor { actor =>
      actor ! Append("productive!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is productive!")
      }
    }
  }

  // This test needs the database fixture
  "Test code" should "be readable" in {
    withDatabase { futureDb =>
      futureDb map { db =>
        db.append("readable!")
        assert(db.toString == "ScalaTest is readable!")
      }
    }
  }

  // This test needs both the actor and the database
  it should "be clear and concise" in {
    withDatabase { futureDb =>
      withActor { actor => // loan-fixture methods compose
        actor ! Append("concise!")
        val futureString = actor ? GetValue
        val futurePair: Future[(Db, String)] =
          futureDb zip futureString
        futurePair map { case (db, s) =>
          db.append("clear!")
          assert(db.toString == "ScalaTest is clear!")
          assert(s == "ScalaTest is concise!")
        }
      }
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating databases, it is a good idea to give each database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.AsyncTestSuite and overriding withFixture(OneArgAsyncTest). Each test in a fixture.AsyncTestSuite takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgAsyncTest. This withFixture method is responsible for invoking the one-arg async test function, so you can perform fixture set up before invoking and passing the fixture into the test function, and ensure clean up is performed after the test completes.

To enable the stacking of traits that define withFixture(NoArgAsyncTest), it is a good idea to let withFixture(NoArgAsyncTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgAsyncTest to a NoArgAsyncTest. You can do that by passing the fixture object to the toNoArgAsyncTest method of OneArgAsyncTest. In other words, instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgAsyncTest) method of the same instance by writing:

withFixture(test.toNoArgAsyncTest(theFixture))

Here's a complete example:

package org.scalatest.examples.asyncflatspec.oneargasynctest

import org.scalatest._
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSpec extends fixture.AsyncFlatSpec {

  type FixtureParam = StringActor

  def withFixture(test: OneArgAsyncTest): FutureOutcome = {

    val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is ") // set up the fixture
      withFixture(test.toNoArgAsyncTest(actor))
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  "Testing" should "be easy" in { actor =>
    actor ! Append("easy!")
    val futureString = actor ? GetValue
    futureString map { s =>
      assert(s == "ScalaTest is easy!")
    }
  }

  it should "be fun" in { actor =>
    actor ! Append("fun!")
    val futureString = actor ? GetValue
    futureString map { s =>
      assert(s == "ScalaTest is fun!")
    }
  }
}

In this example, the tests required one fixture object, a StringActor. If your tests need multiple fixture objects, you can simply define the FixtureParam type to be a tuple containing the objects or, alternatively, a case class containing the objects. For more information on the withFixture(OneArgAsyncTest) technique, see the documentation for fixture.AsyncFlatSpec.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.asyncflatspec.beforeandafter

import org.scalatest.AsyncFlatSpec
import org.scalatest.BeforeAndAfter
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSpec extends AsyncFlatSpec with BeforeAndAfter {

  final val actor = new StringActor

  before {
    actor ! Append("ScalaTest is ") // set up the fixture
  }

  after {
    actor ! Clear // clean up the fixture
  }

  "Testing" should "be easy" in {
    actor ! Append("easy!")
    val futureString = actor ? GetValue
    futureString map { s =>
      assert(s == "ScalaTest is easy!")
    }
  }

  it should "be fun" in {
    actor ! Append("fun!")
    val futureString = actor ? GetValue
    futureString map { s =>
      assert(s == "ScalaTest is fun!")
    }
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state.

Note that on the JVM, if you override ScalaTest's default serial execution context, you will likely need to worry about synchronizing access to shared mutable fixture state, because the execution context may assign different threads to process different Future transformations. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, it can be difficult to spot cases where these constraints are violated. The best approach is to use only immutable objects when transforming Futures. When that's not practical, involve only thread-safe mutable objects, as is done in the above example. On Scala.js, by contrast, you need not worry about thread synchronization, because in effect only one thread exists.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilderActor and StringBufferActor fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.asyncflatspec.composingwithasyncfixture

import org.scalatest._
import org.scalatest.SuiteMixin
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val builderActor = new StringBuilderActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    builderActor ! Append("ScalaTest is ")
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      builderActor ! Clear
    }
  }
}

trait Buffer extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val bufferActor = new StringBufferActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      bufferActor ! Clear
    }
  }
}

class ExampleSpec extends AsyncFlatSpec with Builder with Buffer {

  "Testing" should "be easy" in {
    builderActor ! Append("easy!")
    val futureString = builderActor ? GetValue
    val futureList = bufferActor ? GetValue
    val futurePair: Future[(String, List[String])] = futureString zip futureList
    futurePair map { case (str, lst) =>
      assert(str == "ScalaTest is easy!")
      assert(lst.isEmpty)
      bufferActor ! Append("sweet")
      succeed
    }
  }

  it should "be fun" in {
    builderActor ! Append("fun!")
    val futureString = builderActor ? GetValue
    val futureList = bufferActor ? GetValue
    val futurePair: Future[(String, List[String])] = futureString zip futureList
    futurePair map { case (str, lst) =>
      assert(str == "ScalaTest is fun!")
      assert(lst.isEmpty)
      bufferActor ! Append("awesome")
      succeed
    }
  }
}

By mixing in both the Builder and Buffer traits, ExampleSpec gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Spec extends AsyncFlatSpec with Buffer with Builder

If you only need one fixture you mix in only that trait:

class Example3Spec extends AsyncFlatSpec with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.asyncflatspec.composingbeforeandaftereach

import org.scalatest._
import org.scalatest.BeforeAndAfterEach
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends BeforeAndAfterEach { this: Suite =>

  final val builderActor = new StringBuilderActor

  override def beforeEach() {
    builderActor ! Append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builderActor ! Clear
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  final val bufferActor = new StringBufferActor

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally bufferActor ! Clear
  }
}

class ExampleSpec extends AsyncFlatSpec with Builder with Buffer {

  "Testing" should "be easy" in {
    builderActor ! Append("easy!")
    val futureString = builderActor ? GetValue
    val futureList = bufferActor ? GetValue
    val futurePair: Future[(String, List[String])] = futureString zip futureList
    futurePair map { case (str, lst) =>
      assert(str == "ScalaTest is easy!")
      assert(lst.isEmpty)
      bufferActor ! Append("sweet")
      succeed
    }
  }

  it should "be fun" in {
    builderActor ! Append("fun!")
    val futureString = builderActor ? GetValue
    val futureList = bufferActor ? GetValue
    val futurePair: Future[(String, List[String])] = futureString zip futureList
    futurePair map { case (str, lst) =>
      assert(str == "ScalaTest is fun!")
      assert(lst.isEmpty)
      bufferActor ! Append("awesome")
      succeed
    }
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in an AsyncFlatSpec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any AsyncFlatSpec that uses them, so that the tests they contain will be registered as tests in that AsyncFlatSpec. For example, given this StackActor class:

package org.scalatest.examples.asyncflatspec.sharedtests

import scala.collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Stack operations
case class Push[T](value: T)
sealed abstract class StackOp
case object Pop extends StackOp
case object Peek extends StackOp
case object Size extends StackOp

// Stack info
case class StackInfo[T](top: Option[T], size: Int, max: Int) {
  require(size > 0, "size was less than zero")
  require(max > size, "max was less than size")
  val isFull: Boolean = size == max
  val isEmpty: Boolean = size == 0
}

class StackActor[T](Max: Int, name: String) {

  private final val buf = new ListBuffer[T]

  def !(push: Push[T]): Unit =
    synchronized {
      if (buf.size != Max)
        buf.prepend(push.value)
      else
        throw new IllegalStateException("can't push onto a full stack")
    }

  def ?(op: StackOp)(implicit c: ExecutionContext): Future[StackInfo[T]] =
    synchronized {
      op match {
        case Pop =>
          Future {
            if (buf.size != 0)
              StackInfo(Some(buf.remove(0)), buf.size, Max)
            else
              throw new IllegalStateException("can't pop an empty stack")
          }
        case Peek =>
          Future {
            if (buf.size != 0)
              StackInfo(Some(buf(0)), buf.size, Max)
            else
              throw new IllegalStateException("can't peek an empty stack")
          }
        case Size =>
          Future { StackInfo(None, buf.size, Max) }
      }
    }

  override def toString: String = name
}

You may want to test the stack represented by the StackActor class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several tests that make sense any time the stack is non-empty. Thus you'd ideally want to run those same tests for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these tests out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your AsyncFlatSpec for StackActor, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared tests are run for all three fixtures.

You can define a behavior function that encapsulates these shared tests inside the AsyncFlatSpec that uses them. If they are shared between different AsyncFlatSpecs, however, you could also define them in a separate trait that is mixed into each AsyncFlatSpec that uses them. For example, here the nonEmptyStackActor behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared tests for non-full stacks:

import org.scalatest.AsyncFlatSpec

trait AsyncFlatSpecStackBehaviors { this: AsyncFlatSpec =>

  def nonEmptyStackActor(createNonEmptyStackActor: => StackActor[Int],
        lastItemAdded: Int, name: String): Unit = {

    it should ("return non-empty StackInfo when Size is fired at non-empty stack actor: " + name) in {
      val stackActor = createNonEmptyStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isEmpty)
      }
    }

    it should ("return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: " + name) in {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePeek <- stackActor ? Size
          afterPeek <- stackActor ? Peek
        } yield (beforePeek, afterPeek)
      futurePair map { case (beforePeek, afterPeek) =>
        assert(afterPeek.top == Some(lastItemAdded))
        assert(afterPeek.size == beforePeek.size)
      }
    }

    it should ("return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: " + name) in {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePop <- stackActor ? Size
          afterPop <- stackActor ? Pop
        } yield (beforePop, afterPop)
      futurePair map { case (beforePop, afterPop) =>
        assert(afterPop.top == Some(lastItemAdded))
        assert(afterPop.size == beforePop.size - 1)
      }
    }
  }

  def nonFullStackActor(createNonFullStackActor: => StackActor[Int], name: String): Unit = {

    it should ("return non-full StackInfo when Size is fired at non-full stack actor: " + name) in {
      val stackActor = createNonFullStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isFull)
      }
    }

    it should ("return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: " + name) in {
      val stackActor = createNonFullStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePush <- stackActor ? Size
          afterPush <- { stackActor ! Push(7); stackActor ? Peek }
        } yield (beforePush, afterPush)
      futurePair map { case (beforePush, afterPush) =>
        assert(afterPush.top == Some(7))
        assert(afterPush.size == beforePush.size + 1)
      }
    }
  }
}

Given these behavior functions, you could invoke them directly, but AsyncFlatSpec offers a DSL for the purpose, which looks like this:

it should behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)
it should behave like nonFullStackActor(almostEmptyStackActor, almostEmptyStackActorName)

Here's an example:

class StackSpec extends AsyncFlatSpec with AsyncFlatSpecStackBehaviors {

  val Max = 10
  val LastValuePushed = Max - 1

  // Stack fixture creation methods
  val emptyStackActorName = "empty stack actor"
  def emptyStackActor = new StackActor[Int](Max, emptyStackActorName )

  val fullStackActorName = "full stack actor"
  def fullStackActor = {
    val stackActor = new StackActor[Int](Max, fullStackActorName )
    for (i <- 0 until Max)
      stackActor ! Push(i)
    stackActor
  }

  val almostEmptyStackActorName = "almost empty stack actor"
  def almostEmptyStackActor = {
    val stackActor = new StackActor[Int](Max, almostEmptyStackActorName )
    stackActor ! Push(LastValuePushed)
    stackActor
  }

  val almostFullStackActorName = "almost full stack actor"
  def almostFullStackActor = {
    val stackActor = new StackActor[Int](Max, almostFullStackActorName)
    for (i <- 1 to LastValuePushed)
      stackActor ! Push(i)
    stackActor
  }

  "A Stack actor (when empty)" should "return empty StackInfo when Size is fired at it" in {
    val stackActor = emptyStackActor
    val futureStackInfo = stackActor ? Size
    futureStackInfo map { stackInfo =>
      assert(stackInfo.isEmpty)
    }
  }

  it should "complain when Peek is fired at it" in {
    recoverToSucceededIf[IllegalStateException] {
      emptyStackActor ? Peek
    }
  }

  it should "complain when Pop is fired at it" in {
    recoverToSucceededIf[IllegalStateException] {
      emptyStackActor ? Pop
    }
  }

  "A Stack actor (when non-empty)" should behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)

  it should behave like nonFullStackActor(almostEmptyStackActor, almostEmptyStackActorName)

  it should behave like nonEmptyStackActor(almostFullStackActor, LastValuePushed, almostFullStackActorName)

  it should behave like nonFullStackActor(almostFullStackActor, almostFullStackActorName)

  "A Stack actor (when full)" should "return full StackInfo when Size is fired at it" in {
    val stackActor = fullStackActor
    val futureStackInfo = stackActor ? Size
    futureStackInfo map { stackInfo =>
      assert(stackInfo.isFull)
    }
  }

  it should behave like nonEmptyStackActor(fullStackActor, LastValuePushed, fullStackActorName)

  it should "complain when Push is fired at it" in {
    val stackActor = fullStackActor
    assertThrows[IllegalStateException] {
      stackActor ! Push(10)
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> org.scalatest.run(new StackSpec)
StackSpec:
A Stack actor (when empty)
- should return empty StackInfo when Size is fired at it
- should complain when Peek is fired at it
- should complain when Pop is fired at it
A Stack actor (when non-empty)
- should return non-empty StackInfo when Size is fired at non-empty stack actor: almost empty stack actor
- should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost empty stack actor
- should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost empty stack actor
- should return non-full StackInfo when Size is fired at non-full stack actor: almost empty stack actor
- should return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: almost empty stack actor
- should return non-empty StackInfo when Size is fired at non-empty stack actor: almost full stack actor
- should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost full stack actor
- should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost full stack actor
- should return non-full StackInfo when Size is fired at non-full stack actor: almost full stack actor
- should return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: almost full stack actor
A Stack actor (when full)
- should return full StackInfo when Size is fired at it
- should return non-empty StackInfo when Size is fired at non-empty stack actor: full stack actor
- should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: full stack actor
- should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: full stack actor
- should complain when Push is fired at it

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. Although in an AsyncFlatSpec, the behavior of clause is a nesting construct analogous to AsyncFunSpec's describe clause, you many sometimes need to do a bit of extra work to ensure that the test names are unique. If a duplicate test name problem shows up in an AsyncFlatSpec, you'll need to pass in a prefix or suffix string to add to each test name. You can call toString on the shared fixture object, or pass this string the same way you pass any other data needed by the shared tests. This is the approach taken by the previous AsyncFlatSpecStackBehaviors example.

Given this AsyncFlatSpecStackBehaviors trait, calling it with the almostEmptyStackActor fixture, like this:

"A Stack actor (when non-empty)" should behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)

yields test names:

A Stack actor (when non-empty) should return non-empty StackInfo when Size is fired at non-empty stack actor: almost empty stack actor
A Stack actor (when non-empty) should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost empty stack actor
A Stack actor (when non-empty) should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost empty stack actor

Whereas calling it with the almostFullStackActor fixture, like this:

it should behave like nonEmptyStackActor(almostFullStackActor, LastValuePushed, almostFullStackActorName)

yields different test names:

A Stack actor (when non-empty) should return non-empty StackInfo when Size is fired at non-empty stack actor: almost full stack actor
A Stack actor (when non-empty) should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost full stack actor
A Stack actor (when non-empty) should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost full stack actor

trait AsyncFlatSpecLike extends AsyncTestSuite with AsyncTestRegistration with ShouldVerb with MustVerb with CanVerb with Informing with Notifying with Alerting with Documenting

Implementation trait for class AsyncFlatSpec, which facilitates a “behavior-driven” style of development (BDD), in which tests are combined with text that specifies the behavior the tests verify.

AsyncFlatSpec is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of AsyncFlatSpec into some other class, you can use this trait instead, because class AsyncFlatSpec does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of AsyncFlatSpec.

abstract class AsyncFreeSpec extends AsyncFreeSpecLike

Enables testing of asynchronous code without blocking, using a style consistent with traditional FreeSpec tests.

Recommended Usage: AsyncFreeSpec is intended to enable users of FreeSpec to write non-blocking asynchronous tests that are consistent with their traditional FreeSpec tests. Note: AsyncFreeSpec is intended for use in special situations where non-blocking asynchronous testing is needed, with class FreeSpec used for general needs.

Given a Future returned by the code you are testing, you need not block until the Future completes before performing assertions against its value. You can instead map those assertions onto the Future and return the resulting Future[Assertion] to ScalaTest. The test will complete asynchronously, when the Future[Assertion] completes.

Here's an example AsyncFreeSpec:

package org.scalatest.examples.asyncfreespec

import org.scalatest.AsyncFreeSpec
import scala.concurrent.Future

class AddSpec extends AsyncFreeSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" - {
    "will eventually compute a sum of passed Ints" in {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" - {
    "will immediately compute a sum of passed Ints" in {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

In an AsyncFreeSpec you write a test with a string followed by in and the body of the test in curly braces, like this:

"will eventually compute a sum of passed Ints" in {
  // ...
}

You can nest a test inside any number of description clauses, which you write with a string followed by a dash character and a block, like this:

"addSoon" - {
  // ...
}

You can nest description clauses as deeply as you want. Because the description clause is denoted with an operator, not a word like should, you are free to structure the text however you wish. In short, you structure an AsyncFreeSpec exactly like a FreeSpec, but with tests having result type Assertion or Future[Assertion]. For more examples of structure, see the documentation for FreeSpec.

Starting with version 3.0.0, ScalaTest assertions and matchers have result type Assertion. The result type of the first test in the example above, therefore, is Future[Assertion]. For clarity, here's the relevant code in a REPL session:

scala> import org.scalatest._
import org.scalatest._

scala> import Assertions._
import Assertions._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext
import scala.concurrent.ExecutionContext

scala> implicit val executionContext = ExecutionContext.Implicits.global
executionContext: scala.concurrent.ExecutionContextExecutor = scala.concurrent.impl.ExecutionContextImpl@26141c5b

scala> def addSoon(addends: Int*): Future[Int] = Future { addends.sum }
addSoon: (addends: Int*)scala.concurrent.Future[Int]

scala> val futureSum: Future[Int] = addSoon(1, 2)
futureSum: scala.concurrent.Future[Int] = scala.concurrent.impl.Promise$DefaultPromise@721f47b2

scala> futureSum map { sum => assert(sum == 3) }
res0: scala.concurrent.Future[org.scalatest.Assertion] = scala.concurrent.impl.Promise$DefaultPromise@3955cfcb

The second test has result type Assertion:

scala> def addNow(addends: Int*): Int = addends.sum
addNow: (addends: Int*)Int

scala> val sum: Int = addNow(1, 2)
sum: Int = 3

scala> assert(sum == 3)
res1: org.scalatest.Assertion = Succeeded

When AddSpec is constructed, the second test will be implicitly converted to Future[Assertion] and registered. The implicit conversion is from Assertion to Future[Assertion], so you must end synchronous tests in some ScalaTest assertion or matcher expression. If a test would not otherwise end in type Assertion, you can place succeed at the end of the test. succeed, a field in trait Assertions, returns the Succeeded singleton:

scala> succeed
res2: org.scalatest.Assertion = Succeeded

Thus placing succeed at the end of a test body will satisfy the type checker:

"will immediately compute a sum of passed Ints" - {
  val sum: Int = addNow(1, 2)
  assert(sum == 3)
  println("hi") // println has result type Unit
  succeed       // succeed has result type Assertion
}

An AsyncFreeSpec's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Tests can only be registered with the it method while the AsyncFreeSpec is in its registration phase. Any attempt to register a test after the AsyncFreeSpec has entered its ready phase, i.e., after run has been invoked on the AsyncFreeSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using AsyncFreeSpec is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Asynchronous execution model

AsyncFreeSpec extends AsyncTestSuite, which provides an implicit scala.concurrent.ExecutionContext named executionContext. This execution context is used by AsyncFreeSpec to transform the Future[Assertion]s returned by each test into the FutureOutcome returned by the test function passed to withFixture. This ExecutionContext is also intended to be used in the tests, including when you map assertions onto futures.

On both the JVM and Scala.js, the default execution context provided by ScalaTest's asynchronous testing styles confines execution to a single thread per test. On JavaScript, where single-threaded execution is the only possibility, the default execution context is scala.scalajs.concurrent.JSExecutionContext.Implicits.queue. On the JVM, the default execution context is a serial execution context provided by ScalaTest itself.

When ScalaTest's serial execution context is called upon to execute a task, that task is recorded in a queue for later execution. For example, one task that will be placed in this queue is the task that transforms the Future[Assertion] returned by an asynchronous test body to the FutureOutcome returned from the test function. Other tasks that will be queued are any transformations of, or callbacks registered on, Futures that occur in your test body, including any assertions you map onto Futures. Once the test body returns, the thread that executed the test body will execute the tasks in that queue one after another, in the order they were enqueued.

ScalaTest provides its serial execution context as the default on the JVM for three reasons. First, most often running both tests and suites in parallel does not give a significant performance boost compared to just running suites in parallel. Thus parallel execution of Future transformations within individual tests is not generally needed for performance reasons.

Second, if multiple threads are operating in the same suite concurrently, you'll need to make sure access to any mutable fixture objects by multiple threads is synchronized. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, this does not hold true for callbacks, and in general it is easy to make a mistake. Simply put: synchronizing access to shared mutable state is difficult and error prone. Because ScalaTest's default execution context on the JVM confines execution of Future transformations and call backs to a single thread, you need not (by default) worry about synchronizing access to mutable state in your asynchronous-style tests.

Third, asynchronous-style tests need not be complete when the test body returns, because the test body returns a Future[Assertion]. This Future[Assertion] will often represent a test that has not yet completed. As a result, when using a more traditional execution context backed by a thread-pool, you could potentially start many more tests executing concurrently than there are threads in the thread pool. The more concurrently execute tests you have competing for threads from the same limited thread pool, the more likely it will be that tests will intermitently fail due to timeouts.

Using ScalaTest's serial execution context on the JVM will ensure the same thread that produced the Future[Assertion] returned from a test body is also used to execute any tasks given to the execution context while executing the test body—and that thread will not be allowed to do anything else until the test completes. If the serial execution context's task queue ever becomes empty while the Future[Assertion] returned by that test's body has not yet completed, the thread will block until another task for that test is enqueued. Although it may seem counter-intuitive, this blocking behavior means the total number of tests allowed to run concurrently will be limited to the total number of threads executing suites. This fact means you can tune the thread pool such that maximum performance is reached while avoiding (or at least, reducing the likelihood of) tests that fail due to timeouts because of thread competition.

This thread confinement strategy does mean, however, that when you are using the default execution context on the JVM, you must be sure to never block in the test body waiting for a task to be completed by the execution context. If you block, your test will never complete. This kind of problem will be obvious, because the test will consistently hang every time you run it. (If a test is hanging, and you're not sure which one it is, enable slowpoke notifications.) If you really do want to block in your tests, you may wish to just use a traditional FreeSpec with ScalaFutures instead. Alternatively, you could override the executionContext and use a traditional ExecutionContext backed by a thread pool. This will enable you to block in an asynchronous-style test on the JVM, but you'll need to worry about synchronizing access to shared mutable state.

To use a different execution context, just override executionContext. For example, if you prefer to use the runNow execution context on Scala.js instead of the default queue, you would write:

// on Scala.js
implicit override def executionContext =
    scala.scalajs.concurrent.JSExecutionContext.Implicits.runNow

If you prefer on the JVM to use the global execution context, which is backed by a thread pool, instead of ScalaTest's default serial execution contex, which confines execution to a single thread, you would write:

// on the JVM (and also compiles on Scala.js, giving
// you the queue execution context)
implicit override def executionContext =
    scala.concurrent.ExecutionContext.Implicits.global

Serial and parallel test execution

By default (unless you mix in ParallelTestExecution), tests in an AsyncFreeSpec will be executed one after another, i.e., serially. This is true whether those tests return Assertion or Future[Assertion], no matter what threads are involved. This default behavior allows you to re-use a shared fixture, such as an external database that needs to be cleaned after each test, in multiple tests in async-style suites. This is implemented by registering each test, other than the first test, to run as a continuation after the previous test completes.

If you want the tests of an AsyncFreeSpec to be executed in parallel, you must mix in ParallelTestExecution and enable parallel execution of tests in your build. You enable parallel execution in Runner with the -P command line flag. In the ScalaTest Maven Plugin, set parallel to true. In sbt, parallel execution is the default, but to be explicit you can write:

parallelExecution in Test := true // the default in sbt

On the JVM, if both ParallelTestExecution is mixed in and parallel execution is enabled in the build, tests in an async-style suite will be started in parallel, using threads from the Distributor, and allowed to complete in parallel, using threads from the executionContext. If you are using ScalaTest's serial execution context, the JVM default, asynchronous tests will run in parallel very much like traditional (such as FreeSpec) tests run in parallel: 1) Because ParallelTestExecution extends OneInstancePerTest, each test will run in its own instance of the test class, you need not worry about synchronizing access to mutable instance state shared by different tests in the same suite. 2) Because the serial execution context will confine the execution of each test to the single thread that executes the test body, you need not worry about synchronizing access to shared mutable state accessed by transformations and callbacks of Futures inside the test.

If ParallelTestExecution is mixed in but parallel execution of suites is not enabled, asynchronous tests on the JVM will be started sequentially, by the single thread that invoked run, but without waiting for one test to complete before the next test is started. As a result, asynchronous tests will be allowed to complete in parallel, using threads from the executionContext. If you are using the serial execution context, however, you'll see the same behavior you see when parallel execution is disabled and a traditional suite that mixes in ParallelTestExecution is executed: the tests will run sequentially. If you use an execution context backed by a thread-pool, such as global, however, even though tests will be started sequentially by one thread, they will be allowed to run concurrently using threads from the execution context's thread pool.

The latter behavior is essentially what you'll see on Scala.js when you execute a suite that mixes in ParallelTestExecution. Because only one thread exists when running under JavaScript, you can't "enable parallel execution of suites." However, it may still be useful to run tests in parallel on Scala.js, because tests can invoke API calls that are truly asynchronous by calling into external APIs that take advantage of non-JavaScript threads. Thus on Scala.js, ParallelTestExecution allows asynchronous tests to run in parallel, even though they must be started sequentially. This may give you better performance when you are using API calls in your Scala.js tests that are truly asynchronous.

Futures and expected exceptions

If you need to test for expected exceptions in the context of futures, you can use the recoverToSucceededIf and recoverToExceptionIf methods of trait RecoverMethods. Because this trait is mixed into supertrait AsyncTestSuite, both of these methods are available by default in an AsyncFreeSpec.

If you just want to ensure that a future fails with a particular exception type, and do not need to inspect the exception further, use recoverToSucceededIf:

recoverToSucceededIf[IllegalStateException] { // Result type: Future[Assertion]
  emptyStackActor ? Peek
}

The recoverToSucceededIf method performs a job similar to assertThrows, except in the context of a future. It transforms a Future of any type into a Future[Assertion] that succeeds only if the original future fails with the specified exception. Here's an example in the REPL:

scala> import org.scalatest.RecoverMethods._
import org.scalatest.RecoverMethods._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.ExecutionContext.Implicits.global

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new IllegalStateException }
     | }
res0: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res0.value
res1: Option[scala.util.Try[org.scalatest.Assertion]] = Some(Success(Succeeded))

Otherwise it fails with an error message similar to those given by assertThrows:

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new RuntimeException }
     | }
res2: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res2.value
res3: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but java.lang.RuntimeException
      was thrown))

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { 42 }
     | }
res4: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res4.value
res5: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but no exception was thrown))

The recoverToExceptionIf method differs from the recoverToSucceededIf in its behavior when the assertion succeeds: recoverToSucceededIf yields a Future[Assertion], whereas recoverToExceptionIf yields a Future[T], where T is the expected exception type.

recoverToExceptionIf[IllegalStateException] { // Result type: Future[IllegalStateException]
  emptyStackActor ? Peek
}

In other words, recoverToExpectionIf is to intercept as recovertToSucceededIf is to assertThrows. The first one allows you to perform further assertions on the expected exception. The second one gives you a result type that will satisfy the type checker at the end of the test body. Here's an example showing recoverToExceptionIf in the REPL:

scala> val futureEx =
     |   recoverToExceptionIf[IllegalStateException] {
     |     Future { throw new IllegalStateException("hello") }
     |   }
futureEx: scala.concurrent.Future[IllegalStateException] = ...

scala> futureEx.value
res6: Option[scala.util.Try[IllegalStateException]] =
    Some(Success(java.lang.IllegalStateException: hello))

scala> futureEx map { ex => assert(ex.getMessage == "world") }
res7: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res7.value
res8: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: "[hello]" did not equal "[world]"))

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, AsyncFreeSpec adds a method ignore to strings that can be used instead of in to register a test. For example, to temporarily disable the test with the name "addSoon will eventually compute a sum of passed Ints", just change “in” into “ignore,” like this:

package org.scalatest.examples.asyncfreespec.ignore

import org.scalatest.AsyncFreeSpec
import scala.concurrent.Future

class AddSpec extends AsyncFreeSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" - {
    "will eventually compute a sum of passed Ints" ignore {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" - {
    "will immediately compute a sum of passed Ints" in {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

If you run this version of AddSpec with:

scala> org.scalatest.run(new AddSpec)

It will run only the second test and report that the first test was ignored:

AddSpec:
addSoon
- will eventually compute a sum of passed Ints !!! IGNORED !!!
addNow
- will immediately compute a sum of passed Ints

If you wish to temporarily ignore an entire suite of tests, you can (on the JVM, not Scala.js) annotate the test class with @Ignore, like this:

package org.scalatest.examples.asyncfreespec.ignoreall

import org.scalatest.AsyncFreeSpec
import scala.concurrent.Future
import org.scalatest.Ignore

@Ignore
class AddSpec extends AsyncFreeSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" - {
    "will eventually compute a sum of passed Ints" in {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" - {
    "will immediately compute a sum of passed Ints" in {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the AddSpec in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above AddSpec in the Scala interpreter, you'll see:

AddSpec:
addSoon
- will eventually compute a sum of passed Ints !!! IGNORED !!!
addNow
- will immediately compute a sum of passed Ints !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class visible, to encourage the developers to eventually fix and “un-ignore” it. If you want to prevent a class from being discovered at all (on the JVM, not Scala.js), use the DoNotDiscover annotation instead.

If you want to ignore all tests of a suite on Scala.js, where annotations can't be inspected at runtime, you'll need to change it to ignore at each test site. To make a suite non-discoverable on Scala.js, ensure it does not declare a public no-arg constructor. You can either declare a public constructor that takes one or more arguments, or make the no-arg constructor non-public. Because this technique will also make the suite non-discoverable on the JVM, it is a good approach for suites you want to run (but not be discoverable) on both Scala.js and the JVM.

Informers

One of the parameters to AsyncFreeSpec's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the reporting done by default by AsyncFreeSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event.

One use case for the Informer is to pass more information about a specification to the reporter. For example, the GivenWhenThen trait provides methods that use the implicit info provided by AsyncFreeSpec to pass such information to the reporter. Here's an example:

package org.scalatest.examples.asyncfreespec.info

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncFreeSpec with GivenWhenThen {

  "A mutable Set" - {
    "should allow an element to be added" in {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      info("That's all folks!")
      succeed
    }
  }
}

If you run this AsyncFreeSpec from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSpec)
A mutable Set
- should allow an element to be added
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

Documenters

AsyncFreeSpec also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example AsyncFreeSpec that uses markup:

package org.scalatest.examples.asyncfreespec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncFreeSpec with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

    def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  "A mutable Set" - {
    "should allow an element to be added" in {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      markup("This test finished with a **bold** statement!")
      succeed
    }
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.asyncfreespec.note

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncFreeSpec {

  "A mutable Set" - {
    "should allow an element to be added" in {

      info("info is recorded")
      markup("markup is *also* recorded")
      note("notes are sent immediately")
      alert("alerts are also sent immediately")

      val set = mutable.Set.empty[String]
      set += "clarity"
      assert(set.size === 1)
      assert(set.contains("clarity"))
    }
  }
}

scala> org.scalatest.run(new SetSpec)
SetSpec:
 A mutable Set
   + notes are sent immediately
   + alerts are also sent immediately
 - should allow an element to be added
   + info is recorded
   + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality, has not yet been implemented. Here's an example:

package org.scalatest.examples.asyncfreespec.pending

import org.scalatest.AsyncFreeSpec
import scala.concurrent.Future

class AddSpec extends AsyncFreeSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" - {
    "will eventually compute a sum of passed Ints" in (pending)
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" - {
    "will immediately compute a sum of passed Ints" in {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

(Note: "(pending)" is the body of the test. Thus the test contains just one statement, an invocation of the pending method, which throws TestPendingException.) If you run this version of AddSpec with:

scala> org.scalatest.run(new AddSpec)

It will run both tests, but report that first test is pending. You'll see:

AddSpec:
addSoon
- will eventually compute a sum of passed Ints (pending)
addNow
- will immediately compute a sum of passed Ints

One difference between an ignored test and a pending one is that an ignored test is intended to be used during significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException.

Tagging tests

An AsyncFreeSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing an AsyncFreeSpec, groups of tests can optionally be included and/or excluded. To tag an AsyncFreeSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for AsyncFreeSpecs like this:

package org.scalatest.examples.asyncfreespec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place AsyncFreeSpec tests into groups with tags like this:

import org.scalatest.AsyncFreeSpec
import org.scalatest.tagobjects.Slow
import scala.concurrent.Future

class AddSpec extends AsyncFreeSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" - {
    "will eventually compute a sum of passed Ints" taggedAs(Slow) in {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" - {
    "will immediately compute a sum of passed Ints" taggedAs(Slow, DbTest) in {

      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of an AsyncFreeSpec in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication in async styles:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and eliminate the need to synchronize access to shared mutable state on the JVM.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgAsyncTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgAsyncTest)` instead)
`withFixture(OneArgAsyncTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or a holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.asyncfreespec.getfixture

import org.scalatest.AsyncFreeSpec
import scala.concurrent.Future

class ExampleSpec extends AsyncFreeSpec {

  def fixture: Future[String] = Future { "ScalaTest is " }

  "Testing" - {
    "should be easy" in {
      val future = fixture
      val result = future map { s => s + "easy!" }
      result map { s =>
        assert(s == "ScalaTest is easy!")
      }
    }

    "should be fun" in {
      val future = fixture
      val result = future map { s => s + "fun!" }
      result map { s =>
        assert(s == "ScalaTest is fun!")
      }
    }
  }
}

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, you could pass in an initial value for a fixture object as a parameter to the get-fixture method.

Overriding `withFixture(NoArgAsyncTest)`

Although the get-fixture method approach takes care of setting up a fixture at the beginning of each test, it doesn't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgAsyncTest), a method defined in trait AsyncTestSuite, a supertrait of AsyncFreeSpec.

Trait AsyncFreeSpec's runTest method passes a no-arg async test function to withFixture(NoArgAsyncTest). It is withFixture's responsibility to invoke that test function. The default implementation of withFixture simply invokes the function and returns the result, like this:

// Default implementation in trait AsyncTestSuite
protected def withFixture(test: NoArgAsyncTest): FutureOutcome = {
  test()
}

You can, therefore, override withFixture to perform setup before invoking the test function, and/or perform cleanup after the test completes. The recommended way to ensure cleanup is performed after a test completes is to use the complete-lastly syntax, defined in supertrait CompleteLastly. The complete-lastly syntax will ensure that cleanup will occur whether future-producing code completes abruptly by throwing an exception, or returns normally yielding a future. In the latter case, complete-lastly will register the cleanup code to execute asynchronously when the future completes.

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. In other words, instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  complete {
    super.withFixture(test) // Invoke the test function
  } lastly {
    // Perform cleanup here
  }
}

If you have no cleanup to perform, you can write withFixture like this instead:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  super.withFixture(test) // Invoke the test function
}

If you want to perform an action only for certain outcomes, you'll need to register code performing that action as a callback on the Future using one of Future's registration methods: onComplete, onSuccess, or onFailure. Note that if a test fails, that will be treated as a scala.util.Success(org.scalatest.Failed). So if you want to perform an action if a test fails, for example, you'd register the callback using onSuccess.

Here's an example in which withFixture(NoArgAsyncTest) is used to take a snapshot of the working directory if a test fails, and send that information to the standard output stream:

package org.scalatest.examples.asyncfreespec.noargasynctest

import java.io.File
import org.scalatest._
import scala.concurrent.Future

class ExampleSpec extends AsyncFreeSpec {

  override def withFixture(test: NoArgAsyncTest) = {

    super.withFixture(test) onFailedThen { _ =>
      val currDir = new File(".")
      val fileNames = currDir.list()
      info("Dir snapshot: " + fileNames.mkString(", "))
    }
  }

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "This test" - {
    "should succeed" in {
      addSoon(1, 1) map { sum => assert(sum == 2) }
    }

    "should fail" in {
      addSoon(1, 1) map { sum => assert(sum == 3) }
    }
  }
}

Running this version of ExampleSpec in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSpec)
ExampleSpec:
This test
- should succeed
- should fail *** FAILED ***
  2 did not equal 3 (:33)

Note that the NoArgAsyncTest passed to withFixture, in addition to an apply method that executes the test, also includes the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Lastly, if you want to transform the outcome in some way in withFixture, you'll need to use either the map or transform methods of Future, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  val futureOutcome = super.withFixture(test) // Invoke the test function

  futureOutcome change { outcome =>
    // transform the outcome into a new outcome here
  }
}

Note that a NoArgAsyncTest's apply method will return a scala.util.Failure only if the test completes abruptly with a "test-fatal" exception (such as OutOfMemoryError) that should cause the suite to abort rather than the test to fail. Thus usually you would use map to transform future outcomes, not transform, so that such test-fatal exceptions pass through unchanged. The suite will abort asynchronously with any exception returned from NoArgAsyncTest's apply method in a scala.util.Failure.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

package org.scalatest.examples.asyncfreespec.loanfixture

import java.util.concurrent.ConcurrentHashMap

import scala.concurrent.Future
import scala.concurrent.ExecutionContext

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private final val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer // java.lang.StringBuffer is thread-safe
    databases.put(name, db)
    db
  }
  def removeDb(name: String): Unit = {
    databases.remove(name)
  }
}

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

import org.scalatest._
import DbServer._
import java.util.UUID.randomUUID

class ExampleSpec extends AsyncFreeSpec {

  def withDatabase(testCode: Future[Db] => Future[Assertion]) = {
    val dbName = randomUUID.toString // generate a unique db name
    val futureDb = Future { createDb(dbName) } // create the fixture
    complete {
      val futurePopulatedDb =
        futureDb map { db =>
          db.append("ScalaTest is ") // perform setup
        }
      testCode(futurePopulatedDb) // "loan" the fixture to the test code
    } lastly {
      removeDb(dbName) // ensure the fixture will be cleaned up
    }
  }

  def withActor(testCode: StringActor => Future[Assertion]) = {
    val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is ") // set up the fixture
      testCode(actor) // "loan" the fixture to the test code
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  "Testing" - {
    // This test needs the actor fixture
    "should be productive" in {
      withActor { actor =>
        actor ! Append("productive!")
        val futureString = actor ? GetValue
        futureString map { s =>
          assert(s == "ScalaTest is productive!")
        }
      }
    }
  }

  "Test code" - {
    // This test needs the database fixture
    "should be readable" in {
      withDatabase { futureDb =>
        futureDb map { db =>
          db.append("readable!")
          assert(db.toString == "ScalaTest is readable!")
        }
      }
    }

    // This test needs both the actor and the database
    "should be clear and concise" in {
      withDatabase { futureDb =>
        withActor { actor => // loan-fixture methods compose
          actor ! Append("concise!")
          val futureString = actor ? GetValue
          val futurePair: Future[(Db, String)] =
            futureDb zip futureString
          futurePair map { case (db, s) =>
            db.append("clear!")
            assert(db.toString == "ScalaTest is clear!")
            assert(s == "ScalaTest is concise!")
          }
        }
      }
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating databases, it is a good idea to give each database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.AsyncTestSuite and overriding withFixture(OneArgAsyncTest). Each test in a fixture.AsyncTestSuite takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgAsyncTest. This withFixture method is responsible for invoking the one-arg async test function, so you can perform fixture set up before invoking and passing the fixture into the test function, and ensure clean up is performed after the test completes.

To enable the stacking of traits that define withFixture(NoArgAsyncTest), it is a good idea to let withFixture(NoArgAsyncTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgAsyncTest to a NoArgAsyncTest. You can do that by passing the fixture object to the toNoArgAsyncTest method of OneArgAsyncTest. In other words, instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgAsyncTest) method of the same instance by writing:

withFixture(test.toNoArgAsyncTest(theFixture))

Here's a complete example:

package org.scalatest.examples.asyncfreespec.oneargasynctest

import org.scalatest._
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSpec extends fixture.AsyncFreeSpec {

  type FixtureParam = StringActor

  def withFixture(test: OneArgAsyncTest): FutureOutcome = {

    val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is ") // set up the fixture
      withFixture(test.toNoArgAsyncTest(actor))
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  "Testing" - {
    "should be easy" in { actor =>
      actor ! Append("easy!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is easy!")
      }
    }

    "should be fun" in { actor =>
      actor ! Append("fun!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is fun!")
      }
    }
  }
}

In this example, the tests required one fixture object, a StringActor. If your tests need multiple fixture objects, you can simply define the FixtureParam type to be a tuple containing the objects or, alternatively, a case class containing the objects. For more information on the withFixture(OneArgAsyncTest) technique, see the documentation for fixture.AsyncFreeSpec.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.asyncfreespec.beforeandafter

import org.scalatest.AsyncFreeSpec
import org.scalatest.BeforeAndAfter
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSpec extends AsyncFreeSpec with BeforeAndAfter {

  final val actor = new StringActor

  before {
    actor ! Append("ScalaTest is ") // set up the fixture
  }

  after {
    actor ! Clear // clean up the fixture
  }

  "Testing" - {
    "should be easy" in {
      actor ! Append("easy!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is easy!")
      }
    }

    "should be fun" in {
      actor ! Append("fun!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is fun!")
      }
    }
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state.

Note that on the JVM, if you override ScalaTest's default serial execution context, you will likely need to worry about synchronizing access to shared mutable fixture state, because the execution context may assign different threads to process different Future transformations. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, it can be difficult to spot cases where these constraints are violated. The best approach is to use only immutable objects when transforming Futures. When that's not practical, involve only thread-safe mutable objects, as is done in the above example. On Scala.js, by contrast, you need not worry about thread synchronization, because in effect only one thread exists.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilderActor and StringBufferActor fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.asyncfreespec.composingwithasyncfixture

import org.scalatest._
import org.scalatest.SuiteMixin
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val builderActor = new StringBuilderActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    builderActor ! Append("ScalaTest is ")
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      builderActor ! Clear
    }
  }
}

trait Buffer extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val bufferActor = new StringBufferActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      bufferActor ! Clear
    }
  }
}

class ExampleSpec extends AsyncFreeSpec with Builder with Buffer {

  "Testing" - {
    "should be easy" in {
      builderActor ! Append("easy!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is easy!")
        assert(lst.isEmpty)
        bufferActor ! Append("sweet")
        succeed
      }
    }

    "should be fun" in {
      builderActor ! Append("fun!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is fun!")
        assert(lst.isEmpty)
        bufferActor ! Append("awesome")
        succeed
      }
    }
  }
}

By mixing in both the Builder and Buffer traits, ExampleSpec gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Spec extends AsyncFreeSpec with Buffer with Builder

If you only need one fixture you mix in only that trait:

class Example3Spec extends AsyncFreeSpec with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.asyncfreespec.composingbeforeandaftereach

import org.scalatest._
import org.scalatest.BeforeAndAfterEach
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends BeforeAndAfterEach { this: Suite =>

  final val builderActor = new StringBuilderActor

  override def beforeEach() {
    builderActor ! Append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builderActor ! Clear
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  final val bufferActor = new StringBufferActor

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally bufferActor ! Clear
  }
}

class ExampleSpec extends AsyncFreeSpec with Builder with Buffer {

  "Testing" - {

    "should be easy" in {
      builderActor ! Append("easy!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is easy!")
        assert(lst.isEmpty)
        bufferActor ! Append("sweet")
        succeed
      }
    }

    "should be fun" in {
      builderActor ! Append("fun!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is fun!")
        assert(lst.isEmpty)
        bufferActor ! Append("awesome")
        succeed
      }
    }
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in an AsyncFreeSpec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any AsyncFreeSpec that uses them, so that the tests they contain will be registered as tests in that AsyncFreeSpec. For example, given this StackActor class:

package org.scalatest.examples.asyncfreespec.sharedtests

import scala.collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Stack operations
case class Push[T](value: T)
sealed abstract class StackOp
case object Pop extends StackOp
case object Peek extends StackOp
case object Size extends StackOp

// Stack info
case class StackInfo[T](top: Option[T], size: Int, max: Int) {
  require(size > 0, "size was less than zero")
  require(max >= size, "max was less than size")
  val isFull: Boolean = size == max
  val isEmpty: Boolean = size == 0
}

class StackActor[T](Max: Int, name: String) {

  private final val buf = new ListBuffer[T]

  def !(push: Push[T]): Unit =
    synchronized {
      if (buf.size != Max)
        buf.prepend(push.value)
      else
        throw new IllegalStateException("can't push onto a full stack")
    }

  def ?(op: StackOp)(implicit c: ExecutionContext): Future[StackInfo[T]] =
    synchronized {
      op match {
        case Pop =>
          Future {
            if (buf.size != 0)
              StackInfo(Some(buf.remove(0)), buf.size, Max)
            else
              throw new IllegalStateException("can't pop an empty stack")
          }
        case Peek =>
          Future {
            if (buf.size != 0)
              StackInfo(Some(buf(0)), buf.size, Max)
            else
              throw new IllegalStateException("can't peek an empty stack")
          }
        case Size =>
          Future { StackInfo(None, buf.size, Max) }
      }
    }

  override def toString: String = name
}

You may want to test the stack represented by the StackActor class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several tests that make sense any time the stack is non-empty. Thus you'd ideally want to run those same tests for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these tests out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your AsyncFreeSpec for StackActor, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared tests are run for all three fixtures.

You can define a behavior function that encapsulates these shared tests inside the AsyncFreeSpec that uses them. If they are shared between different AsyncFreeSpecs, however, you could also define them in a separate trait that is mixed into each AsyncFreeSpec that uses them. For example, here the nonEmptyStackActor behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared tests for non-full stacks:

import org.scalatest.AsyncFreeSpec

trait AsyncFreeSpecStackBehaviors { this: AsyncFreeSpec =>

  def nonEmptyStackActor(createNonEmptyStackActor: => StackActor[Int],
        lastItemAdded: Int, name: String): Unit = {

    ("return non-empty StackInfo when Size is fired at non-empty stack actor: " + name) in {
      val stackActor = createNonEmptyStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isEmpty)
      }
    }

    ("return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: " + name) in {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePeek <- stackActor ? Size
          afterPeek <- stackActor ? Peek
        } yield (beforePeek, afterPeek)
      futurePair map { case (beforePeek, afterPeek) =>
        assert(afterPeek.top == Some(lastItemAdded))
        assert(afterPeek.size == beforePeek.size)
      }
    }

    ("return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: " + name) in {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePop <- stackActor ? Size
          afterPop <- stackActor ? Pop
        } yield (beforePop, afterPop)
      futurePair map { case (beforePop, afterPop) =>
        assert(afterPop.top == Some(lastItemAdded))
        assert(afterPop.size == beforePop.size - 1)
      }
    }
  }

  def nonFullStackActor(createNonFullStackActor: => StackActor[Int], name: String): Unit = {

    ("return non-full StackInfo when Size is fired at non-full stack actor: " + name) in {
      val stackActor = createNonFullStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isFull)
      }
    }

    ("return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: " + name) in {
      val stackActor = createNonFullStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePush <- stackActor ? Size
          afterPush <- { stackActor ! Push(7); stackActor ? Peek }
        } yield (beforePush, afterPush)
      futurePair map { case (beforePush, afterPush) =>
        assert(afterPush.top == Some(7))
        assert(afterPush.size == beforePush.size + 1)
      }
    }
  }
}

Given these behavior functions, you could invoke them directly, but AsyncFreeSpec offers a DSL for the purpose, which looks like this:

behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)

Here's an example:

class StackSpec extends AsyncFreeSpec with AsyncFreeSpecStackBehaviors {

  val Max = 10
  val LastValuePushed = Max - 1

  // Stack fixture creation methods
  val emptyStackActorName = "empty stack actor"
  def emptyStackActor = new StackActor[Int](Max, emptyStackActorName )

  val fullStackActorName = "full stack actor"
  def fullStackActor = {
    val stackActor = new StackActor[Int](Max, fullStackActorName )
    for (i <- 0 until Max)
      stackActor ! Push(i)
    stackActor
  }

  val almostEmptyStackActorName = "almost empty stack actor"
  def almostEmptyStackActor = {
    val stackActor = new StackActor[Int](Max, almostEmptyStackActorName )
    stackActor ! Push(LastValuePushed)
    stackActor
  }

  val almostFullStackActorName = "almost full stack actor"
  def almostFullStackActor = {
    val stackActor = new StackActor[Int](Max, almostFullStackActorName)
    for (i <- 1 to LastValuePushed)
      stackActor ! Push(i)
    stackActor
  }

  "A Stack" - {
    "(when empty)" - {
      "should be empty" in {
        val stackActor = emptyStackActor
        val futureStackInfo = stackActor ? Size
        futureStackInfo map { stackInfo =>
          assert(stackInfo.isEmpty)
        }
      }

      "should complain on peek" in {
        recoverToSucceededIf[IllegalStateException] {
          emptyStackActor ? Peek
        }
      }

      "should complain on pop" in {
        recoverToSucceededIf[IllegalStateException] {
          emptyStackActor ? Pop
        }
      }
    }

    "(with one item)" - {
      "should" - {
        behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)
        behave like nonFullStackActor(almostEmptyStackActor, almostEmptyStackActorName)
      }
    }

    "(with one item less than capacity)" - {
      "should" - {
        behave like nonEmptyStackActor(almostFullStackActor, LastValuePushed, almostFullStackActorName)
        behave like nonFullStackActor(almostFullStackActor, almostFullStackActorName)
      }
    }

    "(full)" - {

      "should be full" in {
        val stackActor = fullStackActor
        val futureStackInfo = stackActor ? Size
        futureStackInfo map { stackInfo =>
          assert(stackInfo.isFull)
        }
      }

      "should" - {
        behave like nonEmptyStackActor(fullStackActor, LastValuePushed, fullStackActorName)
      }

      "should complain on a push" in {
        val stackActor = fullStackActor
        assertThrows[IllegalStateException] {
          stackActor ! Push(10)
        }
      }
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> org.scalatest.run(new StackSpec)
StackSpec:
A Stack
  (when empty)
  - should be empty
  - should complain on peek
  - should complain on pop
  (with one item)
    should
    - return non-empty StackInfo when Size is fired at non-empty stack actor: almost empty stack actor
    - return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost empty stack actor
    - return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost empty stack actor
    - return non-full StackInfo when Size is fired at non-full stack actor: almost empty stack actor
    - return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: almost empty stack actor
  (with one item less than capacity)
    should
    - return non-empty StackInfo when Size is fired at non-empty stack actor: almost full stack actor
    - return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost full stack actor
    - return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost full stack actor
    - return non-full StackInfo when Size is fired at non-full stack actor: almost full stack actor
    - return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: almost full stack actor
  (full)
  - should be full
    should
    - return non-empty StackInfo when Size is fired at non-empty stack actor: full stack actor
    - return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: full stack actor
    - return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: full stack actor
  - should complain on a push

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. Although in an AsyncFreeSpec, the - clause is a nesting construct analogous to AsyncFunSpec's describe clause, you many sometimes need to do a bit of extra work to ensure that the test names are unique. If a duplicate test name problem shows up in an AsyncFreeSpec, you'll need to pass in a prefix or suffix string to add to each test name. You can call toString on the shared fixture object, or pass this string the same way you pass any other data needed by the shared tests. This is the approach taken by the previous AsyncFreeSpecStackBehaviors example.

Given this AsyncFreeSpecStackBehaviors trait, calling it with the almostEmptyStackActor fixture, like this:

behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)

yields test names:

A Stack (when non-empty) should return non-empty StackInfo when Size is fired at non-empty stack actor: almost empty stack actor
A Stack (when non-empty) should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost empty stack actor
A Stack (when non-empty) should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost empty stack actor

Whereas calling it with the almostFullStackActor fixture, like this:

behave like nonEmptyStackActor(almostFullStackActor, LastValuePushed, almostFullStackActorName)

yields different test names:

A Stack (when non-empty) should return non-empty StackInfo when Size is fired at non-empty stack actor: almost full stack actor
A Stack (when non-empty) should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost full stack actor
A Stack (when non-empty) should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost full stack actor

trait AsyncFreeSpecLike extends AsyncTestSuite with AsyncTestRegistration with Informing with Notifying with Alerting with Documenting

Implementation trait for class AsyncFreeSpec, which facilitates a “behavior-driven” style of development (BDD), in which tests are nested inside text clauses denoted with the dash operator (-).

AsyncFreeSpec is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of AsyncFreeSpec into some other class, you can use this trait instead, because class AsyncFreeSpec does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of AsyncFreeSpec.

abstract class AsyncFunSpec extends AsyncFunSpecLike

Enables testing of asynchronous code without blocking, using a style consistent with traditional FunSpec tests.

Recommended Usage: AsyncFunSpec is intended to enable users of FunSpec to write non-blocking asynchronous tests that are consistent with their traditional FunSpec tests. Note: AsyncFunSpec is intended for use in special situations where non-blocking asynchronous testing is needed, with class FunSpec used for general needs.

Given a Future returned by the code you are testing, you need not block until the Future completes before performing assertions against its value. You can instead map those assertions onto the Future and return the resulting Future[Assertion] to ScalaTest. The test will complete asynchronously, when the Future[Assertion] completes.

Here's an example AsyncFunSpec:

package org.scalatest.examples.asyncfunspec

import org.scalatest.AsyncFunSpec
import scala.concurrent.Future

class AddSpec extends AsyncFunSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  describe("addSoon") {
    it("will eventually compute a sum of passed Ints") {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  describe("addNow") {
    it("will immediately compute a sum of passed Ints") {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

An AsyncFunSpec contains describe clauses and tests. You define a describe clause with describe, and a test with either it or they. describe, it, and they are methods, defined in AsyncFunSpec, which will be invoked by the primary constructor of AddSpec. A describe clause names, or gives more information about, the subject (class or other entity) you are specifying and testing. In the previous example, "addSoon" and "addNow" are the subjects under specification and test. With each test you provide a string (the spec text) that specifies one bit of behavior of the subject, and a block of code that tests that behavior. You place the spec text between the parentheses, followed by the test code between curly braces. The test code will be wrapped up as a function passed as a by-name parameter to it (or they), which will register the test for later execution.

Note: the they method is intended for use when the subject is plural, for example:

describe("The combinators") {
  they("should be easy to learn") { succeed }
  they("should be efficient") { succeed }
  they("should do something cool") { succeed }
}

Starting with version 3.0.0, ScalaTest assertions and matchers have result type Assertion. The result type of the first test in the example above, therefore, is Future[Assertion]. For clarity, here's the relevant code in a REPL session:

scala> import org.scalatest._
import org.scalatest._

scala> import Assertions._
import Assertions._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext
import scala.concurrent.ExecutionContext

scala> implicit val executionContext = ExecutionContext.Implicits.global
executionContext: scala.concurrent.ExecutionContextExecutor = scala.concurrent.impl.ExecutionContextImpl@26141c5b

scala> def addSoon(addends: Int*): Future[Int] = Future { addends.sum }
addSoon: (addends: Int*)scala.concurrent.Future[Int]

scala> val futureSum: Future[Int] = addSoon(1, 2)
futureSum: scala.concurrent.Future[Int] = scala.concurrent.impl.Promise$DefaultPromise@721f47b2

scala> futureSum map { sum => assert(sum == 3) }
res0: scala.concurrent.Future[org.scalatest.Assertion] = scala.concurrent.impl.Promise$DefaultPromise@3955cfcb

The second test has result type Assertion:

scala> def addNow(addends: Int*): Int = addends.sum
addNow: (addends: Int*)Int

scala> val sum: Int = addNow(1, 2)
sum: Int = 3

scala> assert(sum == 3)
res1: org.scalatest.Assertion = Succeeded

When AddSpec is constructed, the second test will be implicitly converted to Future[Assertion] and registered. The implicit conversion is from Assertion to Future[Assertion], so you must end synchronous tests in some ScalaTest assertion or matcher expression. If a test would not otherwise end in type Assertion, you can place succeed at the end of the test. succeed, a field in trait Assertions, returns the Succeeded singleton:

scala> succeed
res2: org.scalatest.Assertion = Succeeded

Thus placing succeed at the end of a test body will satisfy the type checker:

it("will immediately compute a sum of passed Ints") {
  val sum: Int = addNow(1, 2)
  assert(sum == 3)
  println("hi") // println has result type Unit
  succeed       // succeed has result type Assertion
}

An AsyncFunSpec's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Tests can only be registered with the it method while the AsyncFunSpec is in its registration phase. Any attempt to register a test after the AsyncFunSpec has entered its ready phase, i.e., after run has been invoked on the AsyncFunSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using AsyncFunSpec is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Asynchronous execution model

AsyncFunSpec extends AsyncTestSuite, which provides an implicit scala.concurrent.ExecutionContext named executionContext. This execution context is used by AsyncFunSpec to transform the Future[Assertion]s returned by each test into the FutureOutcome returned by the test function passed to withFixture. This ExecutionContext is also intended to be used in the tests, including when you map assertions onto futures.

On both the JVM and Scala.js, the default execution context provided by ScalaTest's asynchronous testing styles confines execution to a single thread per test. On JavaScript, where single-threaded execution is the only possibility, the default execution context is scala.scalajs.concurrent.JSExecutionContext.Implicits.queue. On the JVM, the default execution context is a serial execution context provided by ScalaTest itself.

When ScalaTest's serial execution context is called upon to execute a task, that task is recorded in a queue for later execution. For example, one task that will be placed in this queue is the task that transforms the Future[Assertion] returned by an asynchronous test body to the FutureOutcome returned from the test function. Other tasks that will be queued are any transformations of, or callbacks registered on, Futures that occur in your test body, including any assertions you map onto Futures. Once the test body returns, the thread that executed the test body will execute the tasks in that queue one after another, in the order they were enqueued.

ScalaTest provides its serial execution context as the default on the JVM for three reasons. First, most often running both tests and suites in parallel does not give a significant performance boost compared to just running suites in parallel. Thus parallel execution of Future transformations within individual tests is not generally needed for performance reasons.

Second, if multiple threads are operating in the same suite concurrently, you'll need to make sure access to any mutable fixture objects by multiple threads is synchronized. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, this does not hold true for callbacks, and in general it is easy to make a mistake. Simply put: synchronizing access to shared mutable state is difficult and error prone. Because ScalaTest's default execution context on the JVM confines execution of Future transformations and call backs to a single thread, you need not (by default) worry about synchronizing access to mutable state in your asynchronous-style tests.

Third, asynchronous-style tests need not be complete when the test body returns, because the test body returns a Future[Assertion]. This Future[Assertion] will often represent a test that has not yet completed. As a result, when using a more traditional execution context backed by a thread-pool, you could potentially start many more tests executing concurrently than there are threads in the thread pool. The more concurrently execute tests you have competing for threads from the same limited thread pool, the more likely it will be that tests will intermitently fail due to timeouts.

Using ScalaTest's serial execution context on the JVM will ensure the same thread that produced the Future[Assertion] returned from a test body is also used to execute any tasks given to the execution context while executing the test body—and that thread will not be allowed to do anything else until the test completes. If the serial execution context's task queue ever becomes empty while the Future[Assertion] returned by that test's body has not yet completed, the thread will block until another task for that test is enqueued. Although it may seem counter-intuitive, this blocking behavior means the total number of tests allowed to run concurrently will be limited to the total number of threads executing suites. This fact means you can tune the thread pool such that maximum performance is reached while avoiding (or at least, reducing the likelihood of) tests that fail due to timeouts because of thread competition.

This thread confinement strategy does mean, however, that when you are using the default execution context on the JVM, you must be sure to never block in the test body waiting for a task to be completed by the execution context. If you block, your test will never complete. This kind of problem will be obvious, because the test will consistently hang every time you run it. (If a test is hanging, and you're not sure which one it is, enable slowpoke notifications.) If you really do want to block in your tests, you may wish to just use a traditional FunSpec with ScalaFutures instead. Alternatively, you could override the executionContext and use a traditional ExecutionContext backed by a thread pool. This will enable you to block in an asynchronous-style test on the JVM, but you'll need to worry about synchronizing access to shared mutable state.

To use a different execution context, just override executionContext. For example, if you prefer to use the runNow execution context on Scala.js instead of the default queue, you would write:

// on Scala.js
implicit override def executionContext =
    scala.scalajs.concurrent.JSExecutionContext.Implicits.runNow

If you prefer on the JVM to use the global execution context, which is backed by a thread pool, instead of ScalaTest's default serial execution contex, which confines execution to a single thread, you would write:

// on the JVM (and also compiles on Scala.js, giving
// you the queue execution context)
implicit override def executionContext =
    scala.concurrent.ExecutionContext.Implicits.global

Serial and parallel test execution

By default (unless you mix in ParallelTestExecution), tests in an AsyncFunSpec will be executed one after another, i.e., serially. This is true whether those tests return Assertion or Future[Assertion], no matter what threads are involved. This default behavior allows you to re-use a shared fixture, such as an external database that needs to be cleaned after each test, in multiple tests in async-style suites. This is implemented by registering each test, other than the first test, to run as a continuation after the previous test completes.

If you want the tests of an AsyncFunSpec to be executed in parallel, you must mix in ParallelTestExecution and enable parallel execution of tests in your build. You enable parallel execution in Runner with the -P command line flag. In the ScalaTest Maven Plugin, set parallel to true. In sbt, parallel execution is the default, but to be explicit you can write:

parallelExecution in Test := true // the default in sbt

On the JVM, if both ParallelTestExecution is mixed in and parallel execution is enabled in the build, tests in an async-style suite will be started in parallel, using threads from the Distributor, and allowed to complete in parallel, using threads from the executionContext. If you are using ScalaTest's serial execution context, the JVM default, asynchronous tests will run in parallel very much like traditional (such as FunSpec) tests run in parallel: 1) Because ParallelTestExecution extends OneInstancePerTest, each test will run in its own instance of the test class, you need not worry about synchronizing access to mutable instance state shared by different tests in the same suite. 2) Because the serial execution context will confine the execution of each test to the single thread that executes the test body, you need not worry about synchronizing access to shared mutable state accessed by transformations and callbacks of Futures inside the test.

If ParallelTestExecution is mixed in but parallel execution of suites is not enabled, asynchronous tests on the JVM will be started sequentially, by the single thread that invoked run, but without waiting for one test to complete before the next test is started. As a result, asynchronous tests will be allowed to complete in parallel, using threads from the executionContext. If you are using the serial execution context, however, you'll see the same behavior you see when parallel execution is disabled and a traditional suite that mixes in ParallelTestExecution is executed: the tests will run sequentially. If you use an execution context backed by a thread-pool, such as global, however, even though tests will be started sequentially by one thread, they will be allowed to run concurrently using threads from the execution context's thread pool.

The latter behavior is essentially what you'll see on Scala.js when you execute a suite that mixes in ParallelTestExecution. Because only one thread exists when running under JavaScript, you can't "enable parallel execution of suites." However, it may still be useful to run tests in parallel on Scala.js, because tests can invoke API calls that are truly asynchronous by calling into external APIs that take advantage of non-JavaScript threads. Thus on Scala.js, ParallelTestExecution allows asynchronous tests to run in parallel, even though they must be started sequentially. This may give you better performance when you are using API calls in your Scala.js tests that are truly asynchronous.

Futures and expected exceptions

If you need to test for expected exceptions in the context of futures, you can use the recoverToSucceededIf and recoverToExceptionIf methods of trait RecoverMethods. Because this trait is mixed into supertrait AsyncTestSuite, both of these methods are available by default in an AsyncFunSpec.

If you just want to ensure that a future fails with a particular exception type, and do not need to inspect the exception further, use recoverToSucceededIf:

recoverToSucceededIf[IllegalStateException] { // Result type: Future[Assertion]
  emptyStackActor ? Peek
}

The recoverToSucceededIf method performs a job similar to assertThrows, except in the context of a future. It transforms a Future of any type into a Future[Assertion] that succeeds only if the original future fails with the specified exception. Here's an example in the REPL:

scala> import org.scalatest.RecoverMethods._
import org.scalatest.RecoverMethods._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.ExecutionContext.Implicits.global

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new IllegalStateException }
     | }
res0: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res0.value
res1: Option[scala.util.Try[org.scalatest.Assertion]] = Some(Success(Succeeded))

Otherwise it fails with an error message similar to those given by assertThrows:

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new RuntimeException }
     | }
res2: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res2.value
res3: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but java.lang.RuntimeException
      was thrown))

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { 42 }
     | }
res4: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res4.value
res5: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but no exception was thrown))

The recoverToExceptionIf method differs from the recoverToSucceededIf in its behavior when the assertion succeeds: recoverToSucceededIf yields a Future[Assertion], whereas recoverToExceptionIf yields a Future[T], where T is the expected exception type.

recoverToExceptionIf[IllegalStateException] { // Result type: Future[IllegalStateException]
  emptyStackActor ? Peek
}

In other words, recoverToExpectionIf is to intercept as recovertToSucceededIf is to assertThrows. The first one allows you to perform further assertions on the expected exception. The second one gives you a result type that will satisfy the type checker at the end of the test body. Here's an example showing recoverToExceptionIf in the REPL:

scala> val futureEx =
     |   recoverToExceptionIf[IllegalStateException] {
     |     Future { throw new IllegalStateException("hello") }
     |   }
futureEx: scala.concurrent.Future[IllegalStateException] = ...

scala> futureEx.value
res6: Option[scala.util.Try[IllegalStateException]] =
    Some(Success(java.lang.IllegalStateException: hello))

scala> futureEx map { ex => assert(ex.getMessage == "world") }
res7: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res7.value
res8: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: "[hello]" did not equal "[world]"))

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, AsyncFunSpec provides registration methods that start with ignore instead of it or they. For example, to temporarily disable the test with the text "will eventually compute a sum of passed Ints", just change “it” into “ignore,” like this:

package org.scalatest.examples.asyncfunspec.ignore

import org.scalatest.AsyncFunSpec
import scala.concurrent.Future

class AddSpec extends AsyncFunSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  describe("addSoon") {
    ignore("will eventually compute a sum of passed Ints") {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  describe("addNow") {
    it("will immediately compute a sum of passed Ints") {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

If you run this version of AddSpec with:

scala> org.scalatest.run(new AddSpec)

It will run only the second test and report that the first test was ignored:

AddSpec:
addSoon
- will eventually compute a sum of passed Ints !!! IGNORED !!!
addNow
- will immediately compute a sum of passed Ints

If you wish to temporarily ignore an entire suite of tests, you can (on the JVM, not Scala.js) annotate the test class with @Ignore, like this:

package org.scalatest.examples.asyncfunspec.ignoreall

import org.scalatest.AsyncFunSpec
import scala.concurrent.Future
import org.scalatest.Ignore

@Ignore
class AddSpec extends AsyncFunSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  describe("addSoon") {
    it("will eventually compute a sum of passed Ints") {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  describe("addNow") {
    it("will immediately compute a sum of passed Ints") {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the AddSpec in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above AddSpec in the Scala interpreter, you'll see:

AddSpec:
addSoon
- will eventually compute a sum of passed Ints !!! IGNORED !!!
addNow
- will immediately compute a sum of passed Ints !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class visible, to encourage the developers to eventually fix and “un-ignore” it. If you want to prevent a class from being discovered at all (on the JVM, not Scala.js), use the DoNotDiscover annotation instead.

If you want to ignore all tests of a suite on Scala.js, where annotations can't be inspected at runtime, you'll need to change it to ignore at each test site. To make a suite non-discoverable on Scala.js, ensure it does not declare a public no-arg constructor. You can either declare a public constructor that takes one or more arguments, or make the no-arg constructor non-public. Because this technique will also make the suite non-discoverable on the JVM, it is a good approach for suites you want to run (but not be discoverable) on both Scala.js and the JVM.

Informers

One of the parameters to AsyncFunSpec's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the reporting done by default by AsyncFunSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via one of its apply methods. The Informer will then pass the information to the Reporter via an InfoProvided event. Here's an example in which the Informer returned by info is used implicitly by the Given, When, and Then methods of trait GivenWhenThen:

package org.scalatest.examples.asyncfunspec.info

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncFunSpec with GivenWhenThen {

  describe("A mutable Set") {
    it("should allow an element to be added") {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      info("That's all folks!")
      succeed
    }
  }
}

If you run this AsyncFunSpec from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSpec)
A mutable Set
- should allow an element to be added
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

Documenters

AsyncFunSpec also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example AsyncFunSpec that uses markup:

package org.scalatest.examples.asyncfunspec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncFunSpec with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

    def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  describe("A mutable Set") {
    it("should allow an element to be added") {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      markup("This test finished with a **bold** statement!")
      succeed
    }
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.asyncfunspec.note

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncFunSpec {

  describe("A mutable Set") {
    it("should allow an element to be added") {

      info("info is recorded")
      markup("markup is *also* recorded")
      note("notes are sent immediately")
      alert("alerts are also sent immediately")

      val set = mutable.Set.empty[String]
      set += "clarity"
      assert(set.size === 1)
      assert(set.contains("clarity"))
    }
  }
}

Because note and alert information is sent immediately, it will appear before the test name in string reporters, and its color will be unrelated to the ultimate outcome of the test: note text will always appear in green, alert text will always appear in yellow. Here's an example:

scala> org.scalatest.run(new SetSpec)
SetSpec:
A mutable Set
  + notes are sent immediately
  + alerts are also sent immediately
- should allow an element to be added
  + info is recorded
  + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality, has not yet been implemented. Here's an example:

package org.scalatest.examples.asyncfunspec.pending

import org.scalatest.AsyncFunSpec
import scala.concurrent.Future

class AddSpec extends AsyncFunSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  describe("addSoon") {
    it("will eventually compute a sum of passed Ints")(pending)
  }

  def addNow(addends: Int*): Int = addends.sum

  describe("addNow") {
    it("will immediately compute a sum of passed Ints") {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

(Note: "(pending)" is the body of the test. Thus the test contains just one statement, an invocation of the pending method, which throws TestPendingException.) If you run this version of AddSpec with:

scala> org.scalatest.run(new AddSpec)

It will run both tests, but report that first test is pending. You'll see:

AddSpec:
addSoon
- will eventually compute a sum of passed Ints (pending)
addNow
- will immediately compute a sum of passed Ints

One difference between an ignored test and a pending one is that an ignored test is intended to be used during significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException.

Tagging tests

An AsyncFunSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing an AsyncFunSpec, groups of tests can optionally be included and/or excluded. To tag an AsyncFunSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for AsyncFunSpecs like this:

package org.scalatest.examples.asyncfunspec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place AsyncFunSpec tests into groups with tags like this:

import org.scalatest.AsyncFunSpec
import org.scalatest.tagobjects.Slow
import scala.concurrent.Future

class AddSpec extends AsyncFunSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  describe("addSoon") {
    it("will eventually compute a sum of passed Ints", Slow) {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  describe("addNow") {
    it("will immediately compute a sum of passed Ints",
      Slow, DbTest) {

      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of an AsyncFunSpec in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication in async styles:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and eliminate the need to synchronize access to shared mutable state on the JVM.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgAsyncTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgAsyncTest)` instead)
`withFixture(OneArgAsyncTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or a holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.asyncfunspec.getfixture

import org.scalatest.AsyncFunSpec
import scala.concurrent.Future

class ExampleSpec extends AsyncFunSpec {

  def fixture: Future[String] = Future { "ScalaTest is " }

  describe("Testing") {
    it("should be easy") {
      val future = fixture
      val result = future map { s => s + "easy!" }
      result map { s =>
        assert(s == "ScalaTest is easy!")
      }
    }

    it("should be fun") {
      val future = fixture
      val result = future map { s => s + "fun!" }
      result map { s =>
        assert(s == "ScalaTest is fun!")
      }
    }
  }
}

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, you could pass in an initial value for a fixture object as a parameter to the get-fixture method.

Overriding `withFixture(NoArgAsyncTest)`

Although the get-fixture method approach takes care of setting up a fixture at the beginning of each test, it doesn't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgAsyncTest), a method defined in trait AsyncTestSuite, a supertrait of AsyncFunSpec.

Trait AsyncFunSpec's runTest method passes a no-arg async test function to withFixture(NoArgAsyncTest). It is withFixture's responsibility to invoke that test function. The default implementation of withFixture simply invokes the function and returns the result, like this:

// Default implementation in trait AsyncTestSuite
protected def withFixture(test: NoArgAsyncTest): FutureOutcome = {
  test()
}

You can, therefore, override withFixture to perform setup before invoking the test function, and/or perform cleanup after the test completes. The recommended way to ensure cleanup is performed after a test completes is to use the complete-lastly syntax, defined in supertrait CompleteLastly. The complete-lastly syntax will ensure that cleanup will occur whether future-producing code completes abruptly by throwing an exception, or returns normally yielding a future. In the latter case, complete-lastly will register the cleanup code to execute asynchronously when the future completes.

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. In other words, instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  complete {
    super.withFixture(test) // Invoke the test function
  } lastly {
    // Perform cleanup here
  }
}

If you have no cleanup to perform, you can write withFixture like this instead:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  super.withFixture(test) // Invoke the test function
}

If you want to perform an action only for certain outcomes, you'll need to register code performing that action as a callback on the Future using one of Future's registration methods: onComplete, onSuccess, or onFailure. Note that if a test fails, that will be treated as a scala.util.Success(org.scalatest.Failed). So if you want to perform an action if a test fails, for example, you'd register the callback using onSuccess.

Here's an example in which withFixture(NoArgAsyncTest) is used to take a snapshot of the working directory if a test fails, and send that information to the standard output stream:

package org.scalatest.examples.asyncfunspec.noargasynctest

import java.io.File
import org.scalatest._
import scala.concurrent.Future

class ExampleSpec extends AsyncFunSpec {

  override def withFixture(test: NoArgAsyncTest) = {

    super.withFixture(test) onFailedThen { _ =>
      val currDir = new File(".")
      val fileNames = currDir.list()
      info("Dir snapshot: " + fileNames.mkString(", "))
    }
  }

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  describe("This test") {
    it("should succeed") {
      addSoon(1, 1) map { sum => assert(sum == 2) }
    }

  it("should fail") {
      addSoon(1, 1) map { sum => assert(sum == 3) }
    }
  }
}

Running this version of ExampleSpec in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSpec)
ExampleSpec:
This test
- should succeed
- should fail *** FAILED ***
  2 did not equal 3 (:33)

Note that the NoArgAsyncTest passed to withFixture, in addition to an apply method that executes the test, also includes the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Lastly, if you want to transform the outcome in some way in withFixture, you'll need to use either the map or transform methods of Future, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  val futureOutcome = super.withFixture(test) // Invoke the test function

  futureOutcome change { outcome =>
    // transform the outcome into a new outcome here
  }
}

Note that a NoArgAsyncTest's apply method will return a scala.util.Failure only if the test completes abruptly with a "test-fatal" exception (such as OutOfMemoryError) that should cause the suite to abort rather than the test to fail. Thus usually you would use map to transform future outcomes, not transform, so that such test-fatal exceptions pass through unchanged. The suite will abort asynchronously with any exception returned from NoArgAsyncTest's apply method in a scala.util.Failure.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

package org.scalatest.examples.asyncfunspec.loanfixture

import java.util.concurrent.ConcurrentHashMap

import scala.concurrent.Future
import scala.concurrent.ExecutionContext

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private final val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer // java.lang.StringBuffer is thread-safe
    databases.put(name, db)
    db
  }
  def removeDb(name: String): Unit = {
    databases.remove(name)
  }
}

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

import org.scalatest._
import DbServer._
import java.util.UUID.randomUUID

class ExampleSpec extends AsyncFunSpec {

  def withDatabase(testCode: Future[Db] => Future[Assertion]) = {
    val dbName = randomUUID.toString // generate a unique db name
    val futureDb = Future { createDb(dbName) } // create the fixture
    complete {
      val futurePopulatedDb =
        futureDb map { db =>
          db.append("ScalaTest is ") // perform setup
        }
      testCode(futurePopulatedDb) // "loan" the fixture to the test code
    } lastly {
      removeDb(dbName) // ensure the fixture will be cleaned up
    }
  }

  def withActor(testCode: StringActor => Future[Assertion]) = {
    val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is ") // set up the fixture
      testCode(actor) // "loan" the fixture to the test code
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  describe("Testing") {
    // This test needs the actor fixture
    it("should be productive") {
      withActor { actor =>
        actor ! Append("productive!")
        val futureString = actor ? GetValue
        futureString map { s =>
          assert(s == "ScalaTest is productive!")
        }
      }
    }
  }

describe("Test code") {
    // This test needs the database fixture
    it("should be readable") {
      withDatabase { futureDb =>
        futureDb map { db =>
          db.append("readable!")
          assert(db.toString == "ScalaTest is readable!")
        }
      }
    }

// This test needs both the actor and the database
    it("should be clear and concise") {
      withDatabase { futureDb =>
        withActor { actor => // loan-fixture methods compose
          actor ! Append("concise!")
          val futureString = actor ? GetValue
          val futurePair: Future[(Db, String)] =
            futureDb zip futureString
          futurePair map { case (db, s) =>
            db.append("clear!")
            assert(db.toString == "ScalaTest is clear!")
            assert(s == "ScalaTest is concise!")
          }
        }
      }
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating databases, it is a good idea to give each database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.AsyncTestSuite and overriding withFixture(OneArgAsyncTest). Each test in a fixture.AsyncTestSuite takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgAsyncTest. This withFixture method is responsible for invoking the one-arg async test function, so you can perform fixture set up before invoking and passing the fixture into the test function, and ensure clean up is performed after the test completes.

To enable the stacking of traits that define withFixture(NoArgAsyncTest), it is a good idea to let withFixture(NoArgAsyncTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgAsyncTest to a NoArgAsyncTest. You can do that by passing the fixture object to the toNoArgAsyncTest method of OneArgAsyncTest. In other words, instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgAsyncTest) method of the same instance by writing:

withFixture(test.toNoArgAsyncTest(theFixture))

Here's a complete example:

package org.scalatest.examples.asyncfunspec.oneargasynctest

import org.scalatest._
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSpec extends fixture.AsyncFunSpec {

  type FixtureParam = StringActor

  def withFixture(test: OneArgAsyncTest): FutureOutcome = {

  val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is ") // set up the fixture
      withFixture(test.toNoArgAsyncTest(actor))
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  describe("Testing") {
    it("should be easy") { actor =>
      actor ! Append("easy!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is easy!")
      }
    }

    it("should be fun") { actor =>
      actor ! Append("fun!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is fun!")
      }
    }
  }
}

In this example, the tests required one fixture object, a StringActor. If your tests need multiple fixture objects, you can simply define the FixtureParam type to be a tuple containing the objects or, alternatively, a case class containing the objects. For more information on the withFixture(OneArgAsyncTest) technique, see the documentation for fixture.AsyncFunSpec.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.asyncfunspec.beforeandafter

import org.scalatest.AsyncFunSpec
import org.scalatest.BeforeAndAfter
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSpec extends AsyncFunSpec with BeforeAndAfter {

  final val actor = new StringActor

  before {
    actor ! Append("ScalaTest is ") // set up the fixture
  }

  after {
    actor ! Clear // clean up the fixture
  }

  describe("Testing") {
    it("should be easy") {
      actor ! Append("easy!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is easy!")
      }
    }

    it("should be fun") {
      actor ! Append("fun!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is fun!")
      }
    }
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state.

Note that on the JVM, if you override ScalaTest's default serial execution context, you will likely need to worry about synchronizing access to shared mutable fixture state, because the execution context may assign different threads to process different Future transformations. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, it can be difficult to spot cases where these constraints are violated. The best approach is to use only immutable objects when transforming Futures. When that's not practical, involve only thread-safe mutable objects, as is done in the above example. On Scala.js, by contrast, you need not worry about thread synchronization, because in effect only one thread exists.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilderActor and StringBufferActor fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.asyncfunspec.composingwithasyncfixture

import org.scalatest._
import org.scalatest.SuiteMixin
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

final val builderActor = new StringBuilderActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    builderActor ! Append("ScalaTest is ")
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      builderActor ! Clear
    }
  }
}

trait Buffer extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val bufferActor = new StringBufferActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      bufferActor ! Clear
    }
  }
}

class ExampleSpec extends AsyncFunSpec with Builder with Buffer {

  describe("Testing") {
    it("should be easy") {
      builderActor ! Append("easy!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is easy!")
        assert(lst.isEmpty)
        bufferActor ! Append("sweet")
        succeed
      }
    }

    it("should be fun") {
      builderActor ! Append("fun!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is fun!")
        assert(lst.isEmpty)
        bufferActor ! Append("awesome")
        succeed
      }
    }
  }
}

By mixing in both the Builder and Buffer traits, ExampleSpec gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Spec extends AsyncFunSpec with Buffer with Builder

If you only need one fixture you mix in only that trait:

class Example3Spec extends AsyncFunSpec with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.asyncfunspec.composingbeforeandaftereach

import org.scalatest._
import org.scalatest.BeforeAndAfterEach
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends BeforeAndAfterEach { this: Suite =>

  final val builderActor = new StringBuilderActor

  override def beforeEach() {
    builderActor ! Append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builderActor ! Clear
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  final val bufferActor = new StringBufferActor

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally bufferActor ! Clear
  }
}

class ExampleSpec extends AsyncFunSpec with Builder with Buffer {

  describe("Testing") {

    it("should be easy") {
      builderActor ! Append("easy!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is easy!")
        assert(lst.isEmpty)
        bufferActor ! Append("sweet")
        succeed
      }
    }

    it("should be fun") {
      builderActor ! Append("fun!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is fun!")
        assert(lst.isEmpty)
        bufferActor ! Append("awesome")
        succeed
      }
    }
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in an AsyncFunSpec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any AsyncFunSpec that uses them, so that the tests they contain will be registered as tests in that AsyncFunSpec. For example, given this StackActor class:

package org.scalatest.examples.asyncfunspec.sharedtests

import scala.collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Stack operations
case class Push[T](value: T)
sealed abstract class StackOp
case object Pop extends StackOp
case object Peek extends StackOp
case object Size extends StackOp

// Stack info
case class StackInfo[T](top: Option[T], size: Int, max: Int) {
  require(size > 0, "size was less than zero")
  require(max > size, "max was less than size")
  val isFull: Boolean = size == max
  val isEmpty: Boolean = size == 0
}

class StackActor[T](Max: Int, name: String) {

  private final val buf = new ListBuffer[T]

  def !(push: Push[T]): Unit =
    synchronized {
      if (buf.size != Max)
        buf.prepend(push.value)
      else
        throw new IllegalStateException("can't push onto a full stack")
    }

  def ?(op: StackOp)(implicit c: ExecutionContext): Future[StackInfo[T]] =
    synchronized {
      op match {
        case Pop =>
          Future {
            if (buf.size != 0)
              StackInfo(Some(buf.remove(0)), buf.size, Max)
            else
              throw new IllegalStateException("can't pop an empty stack")
          }
        case Peek =>
          Future {
            if (buf.size != 0)
              StackInfo(Some(buf(0)), buf.size, Max)
            else
              throw new IllegalStateException("can't peek an empty stack")
          }
        case Size =>
          Future { StackInfo(None, buf.size, Max) }
      }
    }

  override def toString: String = name
}

You may want to test the stack represented by the StackActor class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several tests that make sense any time the stack is non-empty. Thus you'd ideally want to run those same tests for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these tests out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your AsyncFunSpec for StackActor, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared tests are run for all three fixtures.

You can define a behavior function that encapsulates these shared tests inside the AsyncFunSpec that uses them. If they are shared between different AsyncFunSpecs, however, you could also define them in a separate trait that is mixed into each AsyncFunSpec that uses them. For example, here the nonEmptyStackActor behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared tests for non-full stacks:

import org.scalatest.AsyncFunSpec

trait AsyncFunSpecStackBehaviors { this: AsyncFunSpec =>

  def nonEmptyStackActor(createNonEmptyStackActor: => StackActor[Int],
        lastItemAdded: Int, name: String): Unit = {

    it("should return non-empty StackInfo when Size is fired at non-empty stack actor: " + name) {
      val stackActor = createNonEmptyStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isEmpty)
      }
    }

    it("should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: " + name) {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePeek <- stackActor ? Size
          afterPeek <- stackActor ? Peek
        } yield (beforePeek, afterPeek)
      futurePair map { case (beforePeek, afterPeek) =>
        assert(afterPeek.top == Some(lastItemAdded))
        assert(afterPeek.size == beforePeek.size)
      }
    }

    it("should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: " + name) {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePop <- stackActor ? Size
          afterPop <- stackActor ? Pop
        } yield (beforePop, afterPop)
      futurePair map { case (beforePop, afterPop) =>
        assert(afterPop.top == Some(lastItemAdded))
        assert(afterPop.size == beforePop.size - 1)
      }
    }
  }

  def nonFullStackActor(createNonFullStackActor: => StackActor[Int], name: String): Unit = {

    it("should return non-full StackInfo when Size is fired at non-full stack actor: " + name) {
      val stackActor = createNonFullStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isFull)
      }
    }

    it("should return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: " + name) {
      val stackActor = createNonFullStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePush <- stackActor ? Size
          afterPush <- { stackActor ! Push(7); stackActor ? Peek }
        } yield (beforePush, afterPush)
      futurePair map { case (beforePush, afterPush) =>
        assert(afterPush.top == Some(7))
        assert(afterPush.size == beforePush.size + 1)
      }
    }
  }
}

Given these behavior functions, you could invoke them directly, but AsyncFunSpec offers a DSL for the purpose, which looks like this:

it should behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)
it should behave like nonFullStackActor(almostEmptyStackActor, almostEmptyStackActorName)

Here's an example:

class StackSpec extends AsyncFunSpec with AsyncFunSpecStackBehaviors {

  val Max = 10
  val LastValuePushed = Max - 1

  // Stack fixture creation methods
  val emptyStackActorName = "empty stack actor"
  def emptyStackActor = new StackActor[Int](Max, emptyStackActorName )

  val fullStackActorName = "full stack actor"
  def fullStackActor = {
    val stackActor = new StackActor[Int](Max, fullStackActorName )
    for (i <- 0 until Max)
      stackActor ! Push(i)
    stackActor
  }

  val almostEmptyStackActorName = "almost empty stack actor"
  def almostEmptyStackActor = {
    val stackActor = new StackActor[Int](Max, almostEmptyStackActorName )
    stackActor ! Push(LastValuePushed)
    stackActor
  }

  val almostFullStackActorName = "almost full stack actor"
  def almostFullStackActor = {
    val stackActor = new StackActor[Int](Max, almostFullStackActorName)
    for (i <- 1 to LastValuePushed)
      stackActor ! Push(i)
    stackActor
  }

  describe("A Stack") {
    describe("(when empty)") {
      it("should be empty") {
        val stackActor = emptyStackActor
        val futureStackInfo = stackActor ? Size
        futureStackInfo map { stackInfo =>
          assert(stackInfo.isEmpty)
        }
      }

      it("should complain on peek") {
        recoverToSucceededIf[IllegalStateException] {
          emptyStackActor ? Peek
        }
      }

      it("should complain on pop") {
        recoverToSucceededIf[IllegalStateException] {
          emptyStackActor ? Pop
        }
      }
    }

    describe("(when non-empty)") {
      it should behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)
      it should behave like nonFullStackActor(almostEmptyStackActor, almostEmptyStackActorName)
      it should behave like nonEmptyStackActor(almostFullStackActor, LastValuePushed, almostFullStackActorName)
      it should behave like nonFullStackActor(almostFullStackActor, almostFullStackActorName)
    }

    describe("(when full)") {

      it("should be full") {
        val stackActor = fullStackActor
        val futureStackInfo = stackActor ? Size
        futureStackInfo map { stackInfo =>
          assert(stackInfo.isFull)
        }
      }

      it should behave like nonEmptyStackActor(fullStackActor, LastValuePushed, fullStackActorName)

      it("should complain on a push") {
        val stackActor = fullStackActor
        assertThrows[IllegalStateException] {
          stackActor ! Push(10)
        }
      }
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> org.scalatest.run(new StackSpec)
StackSpec:
A Stack
  (when empty)
  - should be empty
  - should complain on peek
  - should complain on pop
  (when non-empty)
  - should return non-empty StackInfo when Size is fired at non-empty stack actor: almost empty stack actor
  - should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost empty stack actor
  - should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost empty stack actor
  - should return non-full StackInfo when Size is fired at non-full stack actor: almost empty stack actor
  - should return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: almost empty stack actor
  - should return non-empty StackInfo when Size is fired at non-empty stack actor: almost full stack actor
  - should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost full stack actor
  - should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost full stack actor
  - should return non-full StackInfo when Size is fired at non-full stack actor: almost full stack actor
  - should return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: almost full stack actor
  (when full)
  - should be full
  - should return non-empty StackInfo when Size is fired at non-empty stack actor: full stack actor
  - should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: full stack actor
  - should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: full stack actor
  - should complain on a push

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. Therefore, you need to do a bit of extra work to ensure that the test names are unique. If a duplicate test name problem shows up in an AsyncFunSpec, you'll need to pass in a prefix or suffix string to add to each test name. You can call toString on the shared fixture object, or pass this string the same way you pass any other data needed by the shared tests. This is the approach taken by the previous AsyncFunSpecStackBehaviors example.

Given this AsyncFunSpecStackBehaviors trait, calling it with the stackWithOneItem fixture, like this:

it should behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)

yields test names:

A Stack (when non-empty) should return non-empty StackInfo when Size is fired at non-empty stack actor: almost empty stack actor
A Stack (when non-empty) should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost empty stack actor
A Stack (when non-empty) should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost empty stack actor

Whereas calling it with the stackWithOneItemLessThanCapacity fixture, like this:

it should behave like nonEmptyStackActor(almostFullStackActor, LastValuePushed, almostFullStackActorName)

yields different test names:

A Stack (when non-empty) should return non-empty StackInfo when Size is fired at non-empty stack actor: almost full stack actor
A Stack (when non-empty) should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost full stack actor
A Stack (when non-empty) should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost full stack actor

trait AsyncFunSpecLike extends AsyncTestSuite with AsyncTestRegistration with Informing with Notifying with Alerting with Documenting

Implementation trait for class AsyncFunSpec, which facilitates a “behavior-driven” style of development (BDD), in which tests are combined with text that specifies the behavior the tests verify.

AsyncFunSpec is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of AsyncFunSpec into some other class, you can use this trait instead, because class AsyncFunSpec does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of AsyncFunSpec.

abstract class AsyncFunSuite extends AsyncFunSuiteLike

Enables testing of asynchronous code without blocking, using a style consistent with traditional FunSuite tests.

Recommended Usage: AsyncFunSuite is intended to enable users of FunSuite to write non-blocking asynchronous tests that are consistent with their traditional FunSuite tests. Note: AsyncFunSuite is intended for use in special situations where non-blocking asynchronous testing is needed, with class FunSuite used for general needs.

Given a Future returned by the code you are testing, you need not block until the Future completes before performing assertions against its value. You can instead map those assertions onto the Future and return the resulting Future[Assertion] to ScalaTest. The test will complete asynchronously, when the Future[Assertion] completes.

Here's an example AsyncFunSuite:

package org.scalatest.examples.asyncfunsuite

import org.scalatest.AsyncFunSuite
import scala.concurrent.Future

class AddSuite extends AsyncFunSuite {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  test("addSoon will eventually compute a sum of passed Ints") {
    val futureSum: Future[Int] = addSoon(1, 2)
    // You can map assertions onto a Future, then return
    // the resulting Future[Assertion] to ScalaTest:
    futureSum map { sum => assert(sum == 3) }
  }

  def addNow(addends: Int*): Int = addends.sum

  test("addNow will immediately compute a sum of passed Ints") {
    val sum: Int = addNow(1, 2)
    // You can also write synchronous tests, which
    // must result in type Assertion:
    assert(sum == 3)
  }
}

“test” is a method, defined in AsyncFunSuite, which will be invoked by the primary constructor of AddSuite. You specify the name of the test as a string between the parentheses, and the test code itself between curly braces. The test code is a function passed as a by-name parameter to test, which registers it for later execution. The result type of the by-name in an AsyncFunSuite must be Future[Assertion].

Starting with version 3.0.0, ScalaTest assertions and matchers have result type Assertion. The result type of the first test in the example above, therefore, is Future[Assertion]. For clarity, here's the relevant code in a REPL session:

scala> import org.scalatest._
import org.scalatest._

scala> import Assertions._
import Assertions._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext
import scala.concurrent.ExecutionContext

scala> implicit val executionContext = ExecutionContext.Implicits.global
executionContext: scala.concurrent.ExecutionContextExecutor = scala.concurrent.impl.ExecutionContextImpl@26141c5b

scala> def addSoon(addends: Int*): Future[Int] = Future { addends.sum }
addSoon: (addends: Int*)scala.concurrent.Future[Int]

scala> val futureSum: Future[Int] = addSoon(1, 2)
futureSum: scala.concurrent.Future[Int] = scala.concurrent.impl.Promise$DefaultPromise@721f47b2

scala> futureSum map { sum => assert(sum == 3) }
res0: scala.concurrent.Future[org.scalatest.Assertion] = scala.concurrent.impl.Promise$DefaultPromise@3955cfcb

The second test has result type Assertion:

scala> def addNow(addends: Int*): Int = addends.sum
addNow: (addends: Int*)Int

scala> val sum: Int = addNow(1, 2)
sum: Int = 3

scala> assert(sum == 3)
res1: org.scalatest.Assertion = Succeeded

When AddSuite is constructed, the second test will be implicitly converted to Future[Assertion] and registered. The implicit conversion is from Assertion to Future[Assertion], so you must end synchronous tests in some ScalaTest assertion or matcher expression. If a test would not otherwise end in type Assertion, you can place succeed at the end of the test. succeed, a field in trait Assertions, returns the Succeeded singleton:

scala> succeed
res2: org.scalatest.Assertion = Succeeded

Thus placing succeed at the end of a test body will satisfy the type checker:

test("addNow will immediately compute a sum of passed Ints") {
  val sum: Int = addNow(1, 2)
  assert(sum == 3)
  println("hi") // println has result type Unit
  succeed       // succeed has result type Assertion
}

An AsyncFunSuite's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Tests can only be registered with the test method while the AsyncFunSuite is in its registration phase. Any attempt to register a test after the AsyncFunSuite has entered its ready phase, i.e., after run has been invoked on the AsyncFunSuite, will be met with a thrown TestRegistrationClosedException. The recommended style of using AsyncFunSuite is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Asynchronous execution model

AsyncFunSuite extends AsyncTestSuite, which provides an implicit scala.concurrent.ExecutionContext named executionContext. This execution context is used by AsyncFunSuite to transform the Future[Assertion]s returned by each test into the FutureOutcome returned by the test function passed to withFixture. This ExecutionContext is also intended to be used in the tests, including when you map assertions onto futures.

On both the JVM and Scala.js, the default execution context provided by ScalaTest's asynchronous testing styles confines execution to a single thread per test. On JavaScript, where single-threaded execution is the only possibility, the default execution context is scala.scalajs.concurrent.JSExecutionContext.Implicits.queue. On the JVM, the default execution context is a serial execution context provided by ScalaTest itself.

When ScalaTest's serial execution context is called upon to execute a task, that task is recorded in a queue for later execution. For example, one task that will be placed in this queue is the task that transforms the Future[Assertion] returned by an asynchronous test body to the FutureOutcome returned from the test function. Other tasks that will be queued are any transformations of, or callbacks registered on, Futures that occur in your test body, including any assertions you map onto Futures. Once the test body returns, the thread that executed the test body will execute the tasks in that queue one after another, in the order they were enqueued.

ScalaTest provides its serial execution context as the default on the JVM for three reasons. First, most often running both tests and suites in parallel does not give a significant performance boost compared to just running suites in parallel. Thus parallel execution of Future transformations within individual tests is not generally needed for performance reasons.

Second, if multiple threads are operating in the same suite concurrently, you'll need to make sure access to any mutable fixture objects by multiple threads is synchronized. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, this does not hold true for callbacks, and in general it is easy to make a mistake. Simply put: synchronizing access to shared mutable state is difficult and error prone. Because ScalaTest's default execution context on the JVM confines execution of Future transformations and call backs to a single thread, you need not (by default) worry about synchronizing access to mutable state in your asynchronous-style tests.

Third, asynchronous-style tests need not be complete when the test body returns, because the test body returns a Future[Assertion]. This Future[Assertion] will often represent a test that has not yet completed. As a result, when using a more traditional execution context backed by a thread-pool, you could potentially start many more tests executing concurrently than there are threads in the thread pool. The more concurrently execute tests you have competing for threads from the same limited thread pool, the more likely it will be that tests will intermitently fail due to timeouts.

Using ScalaTest's serial execution context on the JVM will ensure the same thread that produced the Future[Assertion] returned from a test body is also used to execute any tasks given to the execution context while executing the test body—and that thread will not be allowed to do anything else until the test completes. If the serial execution context's task queue ever becomes empty while the Future[Assertion] returned by that test's body has not yet completed, the thread will block until another task for that test is enqueued. Although it may seem counter-intuitive, this blocking behavior means the total number of tests allowed to run concurrently will be limited to the total number of threads executing suites. This fact means you can tune the thread pool such that maximum performance is reached while avoiding (or at least, reducing the likelihood of) tests that fail due to timeouts because of thread competition.

This thread confinement strategy does mean, however, that when you are using the default execution context on the JVM, you must be sure to never block in the test body waiting for a task to be completed by the execution context. If you block, your test will never complete. This kind of problem will be obvious, because the test will consistently hang every time you run it. (If a test is hanging, and you're not sure which one it is, enable slowpoke notifications.) If you really do want to block in your tests, you may wish to just use a traditional FunSuite with ScalaFutures instead. Alternatively, you could override the executionContext and use a traditional ExecutionContext backed by a thread pool. This will enable you to block in an asynchronous-style test on the JVM, but you'll need to worry about synchronizing access to shared mutable state.

To use a different execution context, just override executionContext. For example, if you prefer to use the runNow execution context on Scala.js instead of the default queue, you would write:

// on Scala.js
implicit override def executionContext =
    scala.scalajs.concurrent.JSExecutionContext.Implicits.runNow

If you prefer on the JVM to use the global execution context, which is backed by a thread pool, instead of ScalaTest's default serial execution contex, which confines execution to a single thread, you would write:

// on the JVM (and also compiles on Scala.js, giving
// you the queue execution context)
implicit override def executionContext =
    scala.concurrent.ExecutionContext.Implicits.global

Serial and parallel test execution

By default (unless you mix in ParallelTestExecution), tests in an AsyncFunSuite will be executed one after another, i.e., serially. This is true whether those tests return Assertion or Future[Assertion], no matter what threads are involved. This default behavior allows you to re-use a shared fixture, such as an external database that needs to be cleaned after each test, in multiple tests in async-style suites. This is implemented by registering each test, other than the first test, to run as a continuation after the previous test completes.

If you want the tests of an AsyncFunSuite to be executed in parallel, you must mix in ParallelTestExecution and enable parallel execution of tests in your build. You enable parallel execution in Runner with the -P command line flag. In the ScalaTest Maven Plugin, set parallel to true. In sbt, parallel execution is the default, but to be explicit you can write:

parallelExecution in Test := true // the default in sbt

On the JVM, if both ParallelTestExecution is mixed in and parallel execution is enabled in the build, tests in an async-style suite will be started in parallel, using threads from the Distributor, and allowed to complete in parallel, using threads from the executionContext. If you are using ScalaTest's serial execution context, the JVM default, asynchronous tests will run in parallel very much like traditional (such as FunSuite) tests run in parallel: 1) Because ParallelTestExecution extends OneInstancePerTest, each test will run in its own instance of the test class, you need not worry about synchronizing access to mutable instance state shared by different tests in the same suite. 2) Because the serial execution context will confine the execution of each test to the single thread that executes the test body, you need not worry about synchronizing access to shared mutable state accessed by transformations and callbacks of Futures inside the test.

If ParallelTestExecution is mixed in but parallel execution of suites is not enabled, asynchronous tests on the JVM will be started sequentially, by the single thread that invoked run, but without waiting for one test to complete before the next test is started. As a result, asynchronous tests will be allowed to complete in parallel, using threads from the executionContext. If you are using the serial execution context, however, you'll see the same behavior you see when parallel execution is disabled and a traditional suite that mixes in ParallelTestExecution is executed: the tests will run sequentially. If you use an execution context backed by a thread-pool, such as global, however, even though tests will be started sequentially by one thread, they will be allowed to run concurrently using threads from the execution context's thread pool.

The latter behavior is essentially what you'll see on Scala.js when you execute a suite that mixes in ParallelTestExecution. Because only one thread exists when running under JavaScript, you can't "enable parallel execution of suites." However, it may still be useful to run tests in parallel on Scala.js, because tests can invoke API calls that are truly asynchronous by calling into external APIs that take advantage of non-JavaScript threads. Thus on Scala.js, ParallelTestExecution allows asynchronous tests to run in parallel, even though they must be started sequentially. This may give you better performance when you are using API calls in your Scala.js tests that are truly asynchronous.

Futures and expected exceptions

If you need to test for expected exceptions in the context of futures, you can use the recoverToSucceededIf and recoverToExceptionIf methods of trait RecoverMethods. Because this trait is mixed into supertrait AsyncTestSuite, both of these methods are available by default in an AsyncFunSuite.

If you just want to ensure that a future fails with a particular exception type, and do not need to inspect the exception further, use recoverToSucceededIf:

recoverToSucceededIf[IllegalStateException] { // Result type: Future[Assertion]
  emptyStackActor ? Peek
}

The recoverToSucceededIf method performs a job similar to assertThrows, except in the context of a future. It transforms a Future of any type into a Future[Assertion] that succeeds only if the original future fails with the specified exception. Here's an example in the REPL:

scala> import org.scalatest.RecoverMethods._
import org.scalatest.RecoverMethods._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.ExecutionContext.Implicits.global

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new IllegalStateException }
     | }
res0: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res0.value
res1: Option[scala.util.Try[org.scalatest.Assertion]] = Some(Success(Succeeded))

Otherwise it fails with an error message similar to those given by assertThrows:

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new RuntimeException }
     | }
res2: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res2.value
res3: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but java.lang.RuntimeException
      was thrown))

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { 42 }
     | }
res4: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res4.value
res5: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but no exception was thrown))

The recoverToExceptionIf method differs from the recoverToSucceededIf in its behavior when the assertion succeeds: recoverToSucceededIf yields a Future[Assertion], whereas recoverToExceptionIf yields a Future[T], where T is the expected exception type.

recoverToExceptionIf[IllegalStateException] { // Result type: Future[IllegalStateException]
  emptyStackActor ? Peek
}

In other words, recoverToExpectionIf is to intercept as recovertToSucceededIf is to assertThrows. The first one allows you to perform further assertions on the expected exception. The second one gives you a result type that will satisfy the type checker at the end of the test body. Here's an example showing recoverToExceptionIf in the REPL:

scala> val futureEx =
     |   recoverToExceptionIf[IllegalStateException] {
     |     Future { throw new IllegalStateException("hello") }
     |   }
futureEx: scala.concurrent.Future[IllegalStateException] = ...

scala> futureEx.value
res6: Option[scala.util.Try[IllegalStateException]] =
    Some(Success(java.lang.IllegalStateException: hello))

scala> futureEx map { ex => assert(ex.getMessage == "world") }
res7: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res7.value
res8: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: "[hello]" did not equal "[world]"))

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, AsyncFunSuite provides registration methods that start with ignore instead of test. Here's an example:

package org.scalatest.examples.asyncfunsuite.ignore

import org.scalatest.AsyncFunSuite
import scala.concurrent.Future

class AddSuite extends AsyncFunSuite {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  ignore("addSoon will eventually compute a sum of passed Ints") {
    val futureSum: Future[Int] = addSoon(1, 2)
    // You can map assertions onto a Future, then return
    // the resulting Future[Assertion] to ScalaTest:
    futureSum map { sum => assert(sum == 3) }
  }

  def addNow(addends: Int*): Int = addends.sum

  test("addNow will immediately compute a sum of passed Ints") {
    val sum: Int = addNow(1, 2)
    // You can also write synchronous tests. The body
    // must have result type Assertion:
    assert(sum == 3)
  }
}

If you run this version of AddSuite with:

scala> org.scalatest.run(new AddSuite)

It will run only the second test and report that the first test was ignored:

AddSuite:
- addSoon will eventually compute a sum of passed Ints !!! IGNORED !!!
- addNow will immediately compute a sum of passed Ints

If you wish to temporarily ignore an entire suite of tests, you can (on the JVM, not Scala.js) annotate the test class with @Ignore, like this:

package org.scalatest.examples.asyncfunsuite.ignoreall

import org.scalatest.AsyncFunSuite
import scala.concurrent.Future
import org.scalatest.Ignore

@Ignore
class AddSuite extends AsyncFunSuite {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  test("addSoon will eventually compute a sum of passed Ints") {
    val futureSum: Future[Int] = addSoon(1, 2)
    // You can map assertions onto a Future, then return
    // the resulting Future[Assertion] to ScalaTest:
    futureSum map { sum => assert(sum == 3) }
  }

  def addNow(addends: Int*): Int = addends.sum

  test("addNow will immediately compute a sum of passed Ints") {
    val sum: Int = addNow(1, 2)
    // You can also write synchronous tests. The body
    // must have result type Assertion:
    assert(sum == 3)
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the AddSuite in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above AddSuite in the Scala interpreter, you'll see:

scala> org.scalatest.run(new AddSuite)
AddSuite:
- addSoon will eventually compute a sum of passed Ints !!! IGNORED !!!
- addNow will immediately compute a sum of passed Ints !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class visible, to encourage the developers to eventually fix and “un-ignore” it. If you want to prevent a class from being discovered at all (on the JVM, not Scala.js), use the DoNotDiscover annotation instead.

If you want to ignore all tests of a suite on Scala.js, where annotations can't be inspected at runtime, you'll need to change test to ignore at each test site. To make a suite non-discoverable on Scala.js, ensure it does not declare a public no-arg constructor. You can either declare a public constructor that takes one or more arguments, or make the no-arg constructor non-public. Because this technique will also make the suite non-discoverable on the JVM, it is a good approach for suites you want to run (but not be discoverable) on both Scala.js and the JVM.

Informers

One of the parameters to AsyncFunSuite's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the reporting done by default by AsyncFunSuite's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event. Here's an example that shows both a direct use as well as an indirect use through the methods of GivenWhenThen:

package org.scalatest.examples.asyncfunsuite.info

import collection.mutable
import org.scalatest._

class SetSuite extends AsyncFunSuite with GivenWhenThen {

  test("An element can be added to an empty mutable Set") {

    Given("an empty mutable Set")
    val set = mutable.Set.empty[String]

    When("an element is added")
    set += "clarity"

    Then("the Set should have size 1")
    assert(set.size === 1)

    And("the Set should contain the added element")
    assert(set.contains("clarity"))

    info("That's all folks!")
    succeed
  }
}

If you run this AsyncFunSuite from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSuite)
SetSuite:
- an element can be added to an empty mutable Set
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

Documenters

AsyncFunSuite also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example AsyncFunSuite that uses markup:

package org.scalatest.examples.asyncfunsuite.markup

import collection.mutable
import org.scalatest._

class SetSuite extends AsyncFunSuite with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

    def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  test("An element can be added to an empty mutable Set") {

    Given("an empty mutable Set")
    val set = mutable.Set.empty[String]

    When("an element is added")
    set += "clarity"

    Then("the Set should have size 1")
    assert(set.size === 1)

    And("the Set should contain the added element")
    assert(set.contains("clarity"))

    markup("This test finished with a **bold** statement!")
    succeed
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.asyncfunsuite.note

import collection.mutable
import org.scalatest._

class SetSuite extends AsyncFunSuite {

  test("An element can be added to an empty mutable Set") {

    info("info is recorded")
    markup("markup is *also* recorded")
    note("notes are sent immediately")
    alert("alerts are also sent immediately")

    val set = mutable.Set.empty[String]
    set += "clarity"
    assert(set.size === 1)
    assert(set.contains("clarity"))
  }
}

Because note and alert information is sent immediately, it will appear before the test name in string reporters, and its color will be unrelated to the ultimate outcome of the test: note text will always appear in green, alert text will always appear in yellow. Here's an example:

scala> org.scalatest.run(new SetSpec)
SetSuite:
  + notes are sent immediately
  + alerts are also sent immediately
- An element can be added to an empty mutable Set
  + info is recorded
  + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality, has not yet been implemented. Here's an example:

package org.scalatest.examples.asyncfunsuite.pending

import org.scalatest.AsyncFunSuite
import scala.concurrent.Future

class AddSuite extends AsyncFunSuite {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  test("addSoon will eventually compute a sum of passed Ints") (pending)

  def addNow(addends: Int*): Int = addends.sum

  test("addNow will immediately compute a sum of passed Ints") {
    val sum: Int = addNow(1, 2)
    // You can also write synchronous tests. The body
    // must have result type Assertion:
    assert(sum == 3)
  }
}

(Note: "(pending)" is the body of the test. Thus the test contains just one statement, an invocation of the pending method, which throws TestPendingException.) If you run this version of AddSuite with:

scala> org.scalatest.run(new AddSuite)

It will run both tests, but report that first test is pending. You'll see:

AddSuite:
- addSoon will eventually compute a sum of passed Ints (pending)
- addNow will immediately compute a sum of passed Ints

One difference between an ignored test and a pending one is that an ignored test is intended to be used during significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException.

Tagging tests

An AsyncFunSuite's tests may be classified into groups by tagging them with string names. As with any suite, when executing an AsyncFunSuite, groups of tests can optionally be included and/or excluded. To tag an AsyncFunSuite's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for AsyncFunSuites like this:

package org.scalatest.examples.asyncfunsuite.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place AsyncFunSuite tests into groups with tags like this:

import org.scalatest.AsyncFunSuite
import org.scalatest.tagobjects.Slow
import scala.concurrent.Future

class AddSuite extends AsyncFunSuite {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  test("addSoon will eventually compute a sum of passed Ints", Slow) {
    val futureSum: Future[Int] = addSoon(1, 2)
    // You can map assertions onto a Future, then return
    // the resulting Future[Assertion] to ScalaTest:
    futureSum map { sum => assert(sum == 3) }
  }

  def addNow(addends: Int*): Int = addends.sum

  test("addNow will immediately compute a sum of passed Ints",
      Slow, DbTest) {

    val sum: Int = addNow(1, 2)
    // You can also write synchronous tests. The body
    // must have result type Assertion:
    assert(sum == 3)
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of an AsyncFunSuite in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication in async styles:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and eliminate the need to synchronize access to shared mutable state on the JVM.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgAsyncTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgAsyncTest)` instead)
`withFixture(OneArgAsyncTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or a holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.asyncfunsuite.getfixture

import org.scalatest.AsyncFunSuite
import collection.mutable.ListBuffer
import scala.concurrent.Future

class ExampleSuite extends AsyncFunSuite {

  def fixture: Future[String] = Future { "ScalaTest is " }

  test("Testing should be easy") {
    val future = fixture
    val result = future map { s => s + "easy!" }
    result map { s =>
      assert(s === "ScalaTest is easy!")
    }
  }

  test("Testing should be fun") {
    val future = fixture
    val result = future map { s => s + "fun!" }
    result map { s =>
      assert(s === "ScalaTest is fun!")
    }
  }
}

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, you could pass in an initial value for a fixture object as a parameter to the get-fixture method.

Overriding `withFixture(NoArgAsyncTest)`

Although the get-fixture method approach takes care of setting up a fixture at the beginning of each test, it doesn't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgAsyncTest), a method defined in trait AsyncTestSuite, a supertrait of AsyncFunSuite.

Trait AsyncFunSuite's runTest method passes a no-arg async test function to withFixture(NoArgAsyncTest). It is withFixture's responsibility to invoke that test function. The default implementation of withFixture simply invokes the function and returns the result, like this:

// Default implementation in trait AsyncTestSuite
protected def withFixture(test: NoArgAsyncTest): FutureOutcome = {
  test()
}

You can, therefore, override withFixture to perform setup before invoking the test function, and/or perform cleanup after the test completes. The recommended way to ensure cleanup is performed after a test completes is to use the complete-lastly syntax, defined in supertrait CompleteLastly. The complete-lastly syntax will ensure that cleanup will occur whether future-producing code completes abruptly by throwing an exception, or returns normally yielding a future. In the latter case, complete-lastly will register the cleanup code to execute asynchronously when the future completes.

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. In other words, instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  complete {
    super.withFixture(test) // Invoke the test function
  } lastly {
    // Perform cleanup here
  }
}

If you have no cleanup to perform, you can write withFixture like this instead:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  super.withFixture(test) // Invoke the test function
}

If you want to perform an action only for certain outcomes, you'll need to register code performing that action as a callback on the Future using one of Future's registration methods: onComplete, onSuccess, or onFailure. Note that if a test fails, that will be treated as a scala.util.Success(org.scalatest.Failed). So if you want to perform an action if a test fails, for example, you'd register the callback using onSuccess.

Here's an example in which withFixture(NoArgAsyncTest) is used to take a snapshot of the working directory if a test fails, and send that information to the standard output stream:

package org.scalatest.examples.asyncfunsuite.noargasynctest

import java.io.File
import org.scalatest._
import scala.concurrent.Future

class ExampleSuite extends AsyncFunSuite {

  override def withFixture(test: NoArgAsyncTest) = {

    super.withFixture(test) onFailedThen { _ =>
      val currDir = new File(".")
      val fileNames = currDir.list()
      info("Dir snapshot: " + fileNames.mkString(", "))
    }
  }

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  test("This test should succeed") {
    addSoon(1, 1) map { sum => assert(sum === 2) }
  }

  test("This test should fail") {
    addSoon(1, 1) map { sum => assert(sum === 3) }
  }
}

Running this version of ExampleSuite in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSuite)
ExampleSuite:
- this test should succeed
Dir snapshot: hello.txt, world.txt
- this test should fail *** FAILED ***
  2 did not equal 3 (:33)

Note that the NoArgAsyncTest passed to withFixture, in addition to an apply method that executes the test, also includes the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Lastly, if you want to transform the outcome in some way in withFixture, you'll need to use either the map or transform methods of Future, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  val futureOutcome = super.withFixture(test) // Invoke the test function

  futureOutcome change { outcome =>
    // transform the outcome into a new outcome here
  }
}

Note that a NoArgAsyncTest's apply method will return a scala.util.Failure only if the test completes abruptly with a "test-fatal" exception (such as OutOfMemoryError) that should cause the suite to abort rather than the test to fail. Thus usually you would use map to transform future outcomes, not transform, so that such test-fatal exceptions pass through unchanged. The suite will abort asynchronously with any exception returned from NoArgAsyncTest's apply method in a scala.util.Failure.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

package org.scalatest.examples.asyncfunsuite.loanfixture

import java.util.concurrent.ConcurrentHashMap

import scala.concurrent.Future
import scala.concurrent.ExecutionContext

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private final val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer // java.lang.StringBuffer is thread-safe
    databases.put(name, db)
    db
  }
  def removeDb(name: String): Unit = {
    databases.remove(name)
  }
}

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

import org.scalatest._
import DbServer._
import java.util.UUID.randomUUID

class ExampleSuite extends AsyncFunSuite {

  def withDatabase(testCode: Future[Db] => Future[Assertion]) = {
    val dbName = randomUUID.toString // generate a unique db name
    val futureDb = Future { createDb(dbName) } // create the fixture
    complete {
      val futurePopulatedDb =
        futureDb map { db =>
          db.append("ScalaTest is ") // perform setup 
        }
      testCode(futurePopulatedDb) // "loan" the fixture to the test code
    } lastly {
      removeDb(dbName) // ensure the fixture will be cleaned up
    }
  }

  def withActor(testCode: StringActor => Future[Assertion]) = {
    val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is ") // set up the fixture
      testCode(actor) // "loan" the fixture to the test code
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  // This test needs the actor fixture
  test("Testing should be productive") {
    withActor { actor =>
      actor ! Append("productive!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s === "ScalaTest is productive!")
      }
    }
  }

  // This test needs the database fixture
  test("Test code should be readable") {
    withDatabase { futureDb =>
      futureDb map { db =>
        db.append("readable!")
        assert(db.toString === "ScalaTest is readable!")
      }
    }
  }

  // This test needs both the actor and the database
  test("Test code should be clear and concise") {
    withDatabase { futureDb =>
      withActor { actor => // loan-fixture methods compose
        actor ! Append("concise!")
        val futureString = actor ? GetValue
        val futurePair: Future[(Db, String)] =
          futureDb zip futureString
        futurePair map { case (db, s) =>
          db.append("clear!")
          assert(db.toString === "ScalaTest is clear!")
          assert(s === "ScalaTest is concise!")
        }
      }
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating databases, it is a good idea to give each database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.AsyncTestSuite and overriding withFixture(OneArgAsyncTest). Each test in a fixture.AsyncTestSuite takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgAsyncTest. This withFixture method is responsible for invoking the one-arg async test function, so you can perform fixture set up before invoking and passing the fixture into the test function, and ensure clean up is performed after the test completes.

To enable the stacking of traits that define withFixture(NoArgAsyncTest), it is a good idea to let withFixture(NoArgAsyncTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgAsyncTest to a NoArgAsyncTest. You can do that by passing the fixture object to the toNoArgAsyncTest method of OneArgAsyncTest. In other words, instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgAsyncTest) method of the same instance by writing:

withFixture(test.toNoArgAsyncTest(theFixture))

Here's a complete example:

package org.scalatest.examples.asyncfunsuite.oneargasynctest

import org.scalatest._
import java.io._
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSuite extends fixture.AsyncFunSuite {

  type FixtureParam = StringActor

  def withFixture(test: OneArgAsyncTest): FutureOutcome = {

    val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is ") // set up the fixture
      withFixture(test.toNoArgAsyncTest(actor))
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  test("Testing should be easy") { actor =>
    actor ! Append("easy!")
    val futureString = actor ? GetValue
    futureString map { s =>
      assert(s === "ScalaTest is easy!")
    }
  }

  test("Testing should be fun") { actor =>
    actor ! Append("fun!")
    val futureString = actor ? GetValue
    futureString map { s =>
      assert(s === "ScalaTest is fun!")
    }
  }
}

In this example, the tests required one fixture object, a StringActor. If your tests need multiple fixture objects, you can simply define the FixtureParam type to be a tuple containing the objects or, alternatively, a case class containing the objects. For more information on the withFixture(OneArgAsyncTest) technique, see the documentation for fixture.AsyncFunSuite.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.asyncfunsuite.beforeandafter

import org.scalatest.AsyncFunSuite
import org.scalatest.BeforeAndAfter
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSuite extends AsyncFunSuite with BeforeAndAfter {

  final val actor = new StringActor

  before {
    actor ! Append("ScalaTest is ") // set up the fixture
  }

  after {
    actor ! Clear // clean up the fixture
  }

  test("testing should be easy") {
    actor ! Append("easy!")
    val futureString = actor ? GetValue
    futureString map { s =>
      assert(s === "ScalaTest is easy!")
    }
  }

  test("testing should be fun") {
    actor ! Append("fun!")
    val futureString = actor ? GetValue
    futureString map { s =>
      assert(s === "ScalaTest is fun!")
    }
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state.

Note that on the JVM, if you override ScalaTest's default serial execution context, you will likely need to worry about synchronizing access to shared mutable fixture state, because the execution context may assign different threads to process different Future transformations. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, it can be difficult to spot cases where these constraints are violated. The best approach is to use only immutable objects when transforming Futures. When that's not practical, involve only thread-safe mutable objects, as is done in the above example. On Scala.js, by contrast, you need not worry about thread synchronization, because in effect only one thread exists.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilderActor and StringBufferActor fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.asyncfunsuite.composingwithasyncfixture

import org.scalatest._
import org.scalatest.SuiteMixin
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val builderActor = new StringBuilderActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    builderActor ! Append("ScalaTest is ")
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      builderActor ! Clear
    }
  }
}

trait Buffer extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val bufferActor = new StringBufferActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      bufferActor ! Clear
    }
  }
}

class ExampleSuite extends AsyncFunSuite with Builder with Buffer {

  test("Testing should be easy") {
    builderActor ! Append("easy!")
    val futureString = builderActor ? GetValue
    val futureList = bufferActor ? GetValue
    val futurePair: Future[(String, List[String])] = futureString zip futureList
    futurePair map { case (str, lst) =>
      assert(str === "ScalaTest is easy!")
      assert(lst.isEmpty)
      bufferActor ! Append("sweet")
      succeed
    }
  }

  test("Testing should be fun") {
    builderActor ! Append("fun!")
    val futureString = builderActor ? GetValue
    val futureList = bufferActor ? GetValue
    val futurePair: Future[(String, List[String])] = futureString zip futureList
    futurePair map { case (str, lst) =>
      assert(str === "ScalaTest is fun!")
      assert(lst.isEmpty)
      bufferActor ! Append("awesome")
      succeed
    }
  }
}

By mixing in both the Builder and Buffer traits, ExampleSuite gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Suite extends AsyncFunSuite with Buffer with Builder

If you only need one fixture you mix in only that trait:

class Example3Suite extends AsyncFunSuite with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.asyncfunsuite.composingbeforeandaftereach

import org.scalatest._
import org.scalatest.BeforeAndAfterEach
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends BeforeAndAfterEach { this: Suite =>

  final val builderActor = new StringBuilderActor

  override def beforeEach() {
    builderActor ! Append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builderActor ! Clear
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  final val bufferActor = new StringBufferActor

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally bufferActor ! Clear
  }
}

class ExampleSuite extends AsyncFunSuite with Builder with Buffer {

  test("Testing should be easy") {
    builderActor ! Append("easy!")
    val futureString = builderActor ? GetValue
    val futureList = bufferActor ? GetValue
    val futurePair: Future[(String, List[String])] = futureString zip futureList
    futurePair map { case (str, lst) =>
      assert(str === "ScalaTest is easy!")
      assert(lst.isEmpty)
      bufferActor ! Append("sweet")
      succeed
    }
  }

  test("Testing should be fun") {
    builderActor ! Append("fun!")
    val futureString = builderActor ? GetValue
    val futureList = bufferActor ? GetValue
    val futurePair: Future[(String, List[String])] = futureString zip futureList
    futurePair map { case (str, lst) =>
      assert(str === "ScalaTest is fun!")
      assert(lst.isEmpty)
      bufferActor ! Append("awesome")
      succeed
    }
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in an AsyncFunSuite, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any AsyncFunSuite that uses them, so that the tests they contain will be registered as tests in that AsyncFunSuite. For example, given this StackActor class:

package org.scalatest.examples.asyncfunsuite.sharedtests

import scala.collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Stack operations
case class Push[T](value: T)
sealed abstract class StackOp
case object Pop extends StackOp
case object Peek extends StackOp
case object Size extends StackOp

// Stack info
case class StackInfo[T](top: Option[T], size: Int, max: Int) {
  require(size >= 0, "size was less than zero")
  require(max >= size, "max was less than size")
  val isFull: Boolean = size == max
  val isEmpty: Boolean = size == 0
}

class StackActor[T](Max: Int, name: String) {

  private final val buf = new ListBuffer[T]

  def !(push: Push[T]): Unit =
    synchronized {
      if (buf.size != Max)
        buf.prepend(push.value)
      else
        throw new IllegalStateException("can't push onto a full stack")
    }

  def ?(op: StackOp)(implicit c: ExecutionContext): Future[StackInfo[T]] =
    synchronized {
      op match {
        case Pop =>
          if (buf.size != 0)
            Future { StackInfo(Some(buf.remove(0)), buf.size, Max) }
          else
            throw new IllegalStateException("can't pop an empty stack")
        case Peek =>
          if (buf.size != 0)
            Future { StackInfo(Some(buf(0)), buf.size, Max) }
          else
            throw new IllegalStateException("can't peek an empty stack")
        case Size =>
          Future { StackInfo(None, buf.size, Max) }
      }
    }

  override def toString: String = name
}

You may want to test the stack represented by the StackActor class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several tests that make sense any time the stack is non-empty. Thus you'd ideally want to run those same tests for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these tests out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your AsyncFunSuite for StackActor, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared tests are run for all three fixtures.

You can define a behavior function that encapsulates these shared tests inside the AsyncFunSuite that uses them. If they are shared between different AsyncFunSuites, however, you could also define them in a separate trait that is mixed into each AsyncFunSuite that uses them. For example, here the nonEmptyStackActor behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared tests for non-full stacks:

import org.scalatest.AsyncFunSuite

trait AsyncFunSuiteStackBehaviors { this: AsyncFunSuite =>

  def nonEmptyStackActor(createNonEmptyStackActor: => StackActor[Int],
        lastItemAdded: Int, name: String): Unit = {

    test("Size is fired at non-empty stack actor: " + name) {
      val stackActor = createNonEmptyStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isEmpty)
      }
    }

    test("Peek is fired at non-empty stack actor: " + name) {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePeek <- stackActor ? Size
          afterPeek <- stackActor ? Peek
        } yield (beforePeek, afterPeek)
      futurePair map { case (beforePeek, afterPeek) =>
        assert(afterPeek.top === Some(lastItemAdded))
        assert(afterPeek.size === beforePeek.size)
      }
    }

    test("Pop is fired at non-empty stack actor: " + name) {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePop <- stackActor ? Size
          afterPop <- stackActor ? Pop
        } yield (beforePop, afterPop)
      futurePair map { case (beforePop, afterPop) =>
        assert(afterPop.top === Some(lastItemAdded))
        assert(afterPop.size === beforePop.size - 1)
      }
    }
  }

  def nonFullStackActor(createNonFullStackActor: => StackActor[Int], name: String): Unit = {

    test("non-full stack actor is not full: " + name) {
      val stackActor = createNonFullStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isFull)
      }
    }

    test("Push is fired at non-full stack actor: " + name) {
      val stackActor = createNonFullStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePush <- stackActor ? Size
          afterPush <- { stackActor ! Push(7); stackActor ? Peek }
        } yield (beforePush, afterPush)
      futurePair map { case (beforePush, afterPush) =>
        assert(afterPush.top === Some(7))
        assert(afterPush.size === beforePush.size + 1)
      }
    }
  }
}

Given these behavior functions, you could invoke them directly, but AsyncFunSuite offers a DSL for the purpose, which looks like this:

testsFor(nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName))
testsFor(nonFullStackActor(almostEmptyStackActor, almostEmptyStackActorName))

Here's an example:

class StackSuite extends AsyncFunSuite with AsyncFunSuiteStackBehaviors {

  val Max = 10
  val LastValuePushed = Max - 1

  // Stack fixture creation methods
  val emptyStackActorName = "empty stack actor"
  def emptyStackActor = new StackActor[Int](Max, emptyStackActorName )

  val fullStackActorName = "full stack actor"
  def fullStackActor = {
    val stackActor = new StackActor[Int](Max, fullStackActorName )
    for (i <- 0 until Max)
      stackActor ! Push(i)
    stackActor
  }

  val almostEmptyStackActorName = "almost empty stack actor"
  def almostEmptyStackActor = {
    val stackActor = new StackActor[Int](Max, almostEmptyStackActorName )
    stackActor ! Push(LastValuePushed)
    stackActor
  }

  val almostFullStackActorName = "almost full stack actor"
  def almostFullStackActor = {
    val stackActor = new StackActor[Int](Max, almostFullStackActorName)
    for (i <- 1 to LastValuePushed)
      stackActor ! Push(i)
    stackActor
  }

  test("an empty stack actor is empty") {
    val stackActor = emptyStackActor
    val futureStackInfo = stackActor ? Size
    futureStackInfo map { stackInfo =>
      assert(stackInfo.isEmpty)
    }
  }

  test("Peek is fired at an empty stack actor") {
    recoverToSucceededIf[IllegalStateException] {
      emptyStackActor ? Peek
    }
  }

  test("Pop is fired at an empty stack actor") {
    recoverToSucceededIf[IllegalStateException] {
      emptyStackActor ? Pop
    }
  }

  testsFor(nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName))
  testsFor(nonFullStackActor(almostEmptyStackActor, almostEmptyStackActorName))

  testsFor(nonEmptyStackActor(almostFullStackActor, LastValuePushed, almostFullStackActorName))
  testsFor(nonFullStackActor(almostFullStackActor, almostFullStackActorName))

  test("a full stack actor is full") {
    val stackActor = fullStackActor
    val futureStackInfo = stackActor ? Size
    futureStackInfo map { stackInfo =>
      assert(stackInfo.isFull)
    }
  }

  testsFor(nonEmptyStackActor(fullStackActor, LastValuePushed, fullStackActorName))

  test("Push is fired at a full stack actor") {
    val stackActor = fullStackActor
    assertThrows[IllegalStateException] {
      stackActor ! Push(10)
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> org.scalatest.run(new StackSuite)
StackSuite:
StackSuite:
- an empty stack actor is empty
- Peek is fired at an empty stack actor
- Pop is fired at an empty stack actor
- Size is fired at non-empty stack actor: almost empty stack actor
- Peek is fired at non-empty stack actor: almost empty stack actor
- Pop is fired at non-empty stack actor: almost empty stack actor
- non-full stack actor is not full: almost empty stack actor
- Push is fired at non-full stack actor: almost empty stack actor
- Size is fired at non-empty stack actor: almost full stack actor
- Peek is fired at non-empty stack actor: almost full stack actor
- Pop is fired at non-empty stack actor: almost full stack actor
- non-full stack actor is not full: almost full stack actor
- Push is fired at non-full stack actor: almost full stack actor
- a full stack actor is full
- Size is fired at non-empty stack actor: full stack actor
- Peek is fired at non-empty stack actor: full stack actor
- Pop is fired at non-empty stack actor: full stack actor
- Push is fired at a full stack actor

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. In a AsyncFunSuite there is no nesting construct analogous to AsyncFunSpec's describe clause. Therefore, you need to do a bit of extra work to ensure that the test names are unique. If a duplicate test name problem shows up in an AsyncFunSuite, you'll need to pass in a prefix or suffix string to add to each test name. You can call toString on the shared fixture object, or pass this string the same way you pass any other data needed by the shared tests. This is the approach taken by the previous AsyncFunSuiteStackBehaviors example.

Given this AsyncFunSuiteStackBehaviors trait, calling it with the stackWithOneItem fixture, like this:

testsFor(nonEmptyStackActor(almostFullStackActor, LastValuePushed, almostFullStackActorName))

yields test names:

Size is fired at non-empty stack actor: almost empty stack actor
Peek is fired at non-empty stack actor: almost empty stack actor
Pop is fired at non-empty stack actor: almost empty stack actor

Whereas calling it with the stackWithOneItemLessThanCapacity fixture, like this:

testsFor(nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed))

yields different test names:

Size is fired at non-empty stack actor: almost full stack actor
Peek is fired at non-empty stack actor: almost full stack actor
Pop is fired at non-empty stack actor: almost full stack actor

trait AsyncFunSuiteLike extends AsyncTestSuite with AsyncTestRegistration with Informing with Notifying with Alerting with Documenting

Implementation trait for class AsyncFunSuite, which represents a suite of tests in which each test is represented as a function value.

AsyncFunSuite is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of AsyncFunSuite into some other class, you can use this trait instead, because class AsyncFunSuite does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of AsyncFunSuite.

trait AsyncTestRegistration extends AnyRef

Trait declaring methods that can be used to register by-name test functions that have result type Future[Assertion].

trait AsyncTestSuite extends Suite with RecoverMethods with CompleteLastly

The base trait of ScalaTest's asynchronous testing styles, which defines a withFixture lifecycle method that accepts as its parameter a test function that returns a FutureOutcome.

The withFixture method add by this trait has the following signature and implementation:

def withFixture(test: NoArgAsyncTest): FutureOutcome = {
  test()
}

This trait enables testing of asynchronous code without blocking. Instead of returning Outcome like TestSuite's withFixture, this trait's withFixture method returns a FutureOutcome. Similarly, the apply method of test function interface, NoArgAsyncTest, returns FutureOutcome:

// In trait NoArgAsyncTest:
def apply(): FutureOutcome

The withFixture method supports async testing, because when the test function returns, the test body has not necessarily finished execution.

The recommended way to ensure cleanup is performed after a test body finishes execution is to use a complete-lastly clause, syntax that is defined in trait CompleteLastly, which this trait extends. Using cleanup-lastly will ensure that cleanup will occur whether FutureOutcome-producing code completes abruptly by throwing an exception, or returns normally yielding a FutureOutcome. In the latter case, complete-lastly will register the cleanup code to execute asynchronously when the FutureOutcome completes.

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. In other words, instead of writing “test()”, you should write “super.withFixture(test)”. Thus, the recommended structure of a withFixture implementation that performs cleanup looks like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {
  // Perform setup here
  complete {
    super.withFixture(test) // Invoke the test function
  } lastly {
    // Perform cleanup here
  }
}

If you have no cleanup to perform, you can write withFixture like this instead:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {
  // Perform setup here
  super.withFixture(test) // Invoke the test function
}

The test function and withFixture method returns a FutureOutcome, a ScalaTest class that wraps a Scala Future[Outcome] and offers methods more specific to asynchronous test outcomes. In a Scala Future, any exception results in a scala.util.Failure. In a FutureOutcome, a thrown TestPendingException always results in a Pending, a thrown TestCanceledException always results in a Canceled, and any other exception, so long as it isn't suite-aborting, results in a Failed. This is true of the asynchronous test code itself that's represented by the FutureOutcome and any transformation or callback registered on the FutureOutcome in withFixture.

If you want to perform an action only for certain outcomes, you'll need to register code performing that action on the FutureOutcome using one of FutureOutcome's callback registration methods:

onSucceededThen - executed if the Outcome is a Succeeded.
onFailedThen - executed if the Outcome is a Failed.
onCanceledThen - executed if the Outcome is a Canceled.
onPendingThen - executed if the Outcome is a Pending.
onOutcomeThen - executed on any Outcome (i.e., no suite-aborting exception is thrown).
onAbortedThen - executed if a suite-aborting exception is thrown.
onCompletedThen - executed whether the result is an Outcome or a thrown suite-aborting exception.

For example, if you want to perform an action if a test fails, you'd register the callback using onFailedThen, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  val futureOutcome = super.withFixture(test) // Invoke the test function

  futureOutcome onFailedThen { ex =>
    // perform action that you want to occur
    // only if a test fails here
  }
}

Note that all callback registration methods, such as onFailedThen used in the previous example, return a new FutureOutcome that won't complete until the the original FutureOutcome and the callback has completed. If the callback throws an exception, the resulting FutureOutcome will represent that exception. For example, if a FutureOutcome results in Failed, but a callback registered on that FutureOutcome with onFailedThen throws TestPendingException, the result of the FutureOutcome returned by onFailedThen will be Pending.

Lastly, if you want to change the outcome in some way in withFixture, you'll need to use the change method of FutureOutcome, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  val futureOutcome = super.withFixture(test) // Invoke the test function

  futureOutcome change { outcome =>
    // transform the outcome into a new outcome here
  }
}

trait AsyncTestSuiteMixin extends SuiteMixin

Trait defining abstract "lifecycle" methods that are implemented in AsyncTestSuite and can be overridden in stackable modification traits.

The main use case for this trait is to override withFixture in a mixin trait. Here's an example:

trait Builder extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val builder = new ThreadSafeStringBuilder

  abstract override def withFixture(test: NoArgAsyncTest) = {
    builder.append("ScalaTest is ")
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      builder.clear()
    }
  }
}

abstract class AsyncWordSpec extends AsyncWordSpecLike

Enables testing of asynchronous code without blocking, using a style consistent with traditional WordSpec tests.

Recommended Usage: AsyncFunSpec is intended to enable users of FunSpec to write non-blocking asynchronous tests that are consistent with their traditional FunSpec tests. Note: AsyncFunSpec is intended for use in special situations where non-blocking asynchronous testing is needed, with class FunSpec used for general needs.

Given a Future returned by the code you are testing, you need not block until the Future completes before performing assertions against its value. You can instead map those assertions onto the Future and return the resulting Future[Assertion] to ScalaTest. The test will complete asynchronously, when the Future[Assertion] completes.

Here's an example AsyncWordSpec:

package org.scalatest.examples.asyncwordspec

import org.scalatest.AsyncWordSpec
import scala.concurrent.Future

class AddSpec extends AsyncWordSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" should {
    "eventually compute a sum of passed Ints" in {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" should {
    "immediately compute a sum of passed Ints" in {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

“it” is a method, defined in AsyncWordSpec, which will be invoked by the primary constructor of AddSpec. You specify the name of the test as a string between the parentheses, and the test code itself between curly braces. The test code is a function passed as a by-name parameter to it, which registers it for later execution. The result type of the by-name in an AsyncWordSpec must be Future[Assertion].

In an AsyncWordSpec you write a one (or more) sentence specification for each bit of behavior you wish to specify and test. Each specification sentence has a "subject," which is sometimes called the system under test (or SUT). The subject is entity being specified and tested and also serves as the subject of the sentences you write for each test. A subject can be followed by one of three verbs, should, must, or can, and a block. Here are some examples:

"A Stack" should {
  // ...
}
"An Account" must {
  // ...
}
"A ShippingManifest" can {
  // ...
}

You can describe a subject in varying situations by using a when clause. A when clause follows the subject and precedes a block. In the block after the when, you place strings that describe a situation or a state the subject may be in using a string, each followed by a verb. Here's an example:

"A Stack" when {
  "empty" should {
    // ...
  }
  "non-empty" should {
    // ...
  }
  "full" should {
    // ...
  }
}

When you are ready to finish a sentence, you write a string followed by in and a block that contains the code of the test. In short, you structure an AsyncWordSpec exactly like a WordSpec, but with tests having result type Assertion or Future[Assertion]. For more examples of structure, see the documentation for WordSpec.

Starting with version 3.0.0, ScalaTest assertions and matchers have result type Assertion. The result type of the first test in the example above, therefore, is Future[Assertion]. For clarity, here's the relevant code in a REPL session:

scala> import org.scalatest._
import org.scalatest._

scala> import Assertions._
import Assertions._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext
import scala.concurrent.ExecutionContext

scala> implicit val executionContext = ExecutionContext.Implicits.global
executionContext: scala.concurrent.ExecutionContextExecutor = scala.concurrent.impl.ExecutionContextImpl@26141c5b

scala> def addSoon(addends: Int*): Future[Int] = Future { addends.sum }
addSoon: (addends: Int*)scala.concurrent.Future[Int]

scala> val futureSum: Future[Int] = addSoon(1, 2)
futureSum: scala.concurrent.Future[Int] = scala.concurrent.impl.Promise$DefaultPromise@721f47b2

scala> futureSum map { sum => assert(sum == 3) }
res0: scala.concurrent.Future[org.scalatest.Assertion] = scala.concurrent.impl.Promise$DefaultPromise@3955cfcb

The second test has result type Assertion:

scala> def addNow(addends: Int*): Int = addends.sum
addNow: (addends: Int*)Int

scala> val sum: Int = addNow(1, 2)
sum: Int = 3

scala> assert(sum == 3)
res1: org.scalatest.Assertion = Succeeded

When AddSpec is constructed, the second test will be implicitly converted to Future[Assertion] and registered. The implicit conversion is from Assertion to Future[Assertion], so you must end synchronous tests in some ScalaTest assertion or matcher expression. If a test would not otherwise end in type Assertion, you can place succeed at the end of the test. succeed, a field in trait Assertions, returns the Succeeded singleton:

scala> succeed
res2: org.scalatest.Assertion = Succeeded

Thus placing succeed at the end of a test body will satisfy the type checker:

"immediately compute a sum of passed Ints" in {
  val sum: Int = addNow(1, 2)
  assert(sum == 3)
  println("hi") // println has result type Unit
  succeed       // succeed has result type Assertion
}

An AsyncWordSpec's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Tests can only be registered with the it method while the AsyncWordSpec is in its registration phase. Any attempt to register a test after the AsyncWordSpec has entered its ready phase, i.e., after run has been invoked on the AsyncWordSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using AsyncWordSpec is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Asynchronous execution model

AsyncWordSpec extends AsyncTestSuite, which provides an implicit scala.concurrent.ExecutionContext named executionContext. This execution context is used by AsyncWordSpec to transform the Future[Assertion]s returned by each test into the FutureOutcome returned by the test function passed to withFixture. This ExecutionContext is also intended to be used in the tests, including when you map assertions onto futures.

On both the JVM and Scala.js, the default execution context provided by ScalaTest's asynchronous testing styles confines execution to a single thread per test. On JavaScript, where single-threaded execution is the only possibility, the default execution context is scala.scalajs.concurrent.JSExecutionContext.Implicits.queue. On the JVM, the default execution context is a serial execution context provided by ScalaTest itself.

When ScalaTest's serial execution context is called upon to execute a task, that task is recorded in a queue for later execution. For example, one task that will be placed in this queue is the task that transforms the Future[Assertion] returned by an asynchronous test body to the FutureOutcome returned from the test function. Other tasks that will be queued are any transformations of, or callbacks registered on, Futures that occur in your test body, including any assertions you map onto Futures. Once the test body returns, the thread that executed the test body will execute the tasks in that queue one after another, in the order they were enqueued.

ScalaTest provides its serial execution context as the default on the JVM for three reasons. First, most often running both tests and suites in parallel does not give a significant performance boost compared to just running suites in parallel. Thus parallel execution of Future transformations within individual tests is not generally needed for performance reasons.

Second, if multiple threads are operating in the same suite concurrently, you'll need to make sure access to any mutable fixture objects by multiple threads is synchronized. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, this does not hold true for callbacks, and in general it is easy to make a mistake. Simply put: synchronizing access to shared mutable state is difficult and error prone. Because ScalaTest's default execution context on the JVM confines execution of Future transformations and call backs to a single thread, you need not (by default) worry about synchronizing access to mutable state in your asynchronous-style tests.

Third, asynchronous-style tests need not be complete when the test body returns, because the test body returns a Future[Assertion]. This Future[Assertion] will often represent a test that has not yet completed. As a result, when using a more traditional execution context backed by a thread-pool, you could potentially start many more tests executing concurrently than there are threads in the thread pool. The more concurrently execute tests you have competing for threads from the same limited thread pool, the more likely it will be that tests will intermitently fail due to timeouts.

Using ScalaTest's serial execution context on the JVM will ensure the same thread that produced the Future[Assertion] returned from a test body is also used to execute any tasks given to the execution context while executing the test body—and that thread will not be allowed to do anything else until the test completes. If the serial execution context's task queue ever becomes empty while the Future[Assertion] returned by that test's body has not yet completed, the thread will block until another task for that test is enqueued. Although it may seem counter-intuitive, this blocking behavior means the total number of tests allowed to run concurrently will be limited to the total number of threads executing suites. This fact means you can tune the thread pool such that maximum performance is reached while avoiding (or at least, reducing the likelihood of) tests that fail due to timeouts because of thread competition.

This thread confinement strategy does mean, however, that when you are using the default execution context on the JVM, you must be sure to never block in the test body waiting for a task to be completed by the execution context. If you block, your test will never complete. This kind of problem will be obvious, because the test will consistently hang every time you run it. (If a test is hanging, and you're not sure which one it is, enable slowpoke notifications.) If you really do want to block in your tests, you may wish to just use a traditional WordSpec with ScalaFutures instead. Alternatively, you could override the executionContext and use a traditional ExecutionContext backed by a thread pool. This will enable you to block in an asynchronous-style test on the JVM, but you'll need to worry about synchronizing access to shared mutable state.

To use a different execution context, just override executionContext. For example, if you prefer to use the runNow execution context on Scala.js instead of the default queue, you would write:

// on Scala.js
implicit override def executionContext =
    scala.scalajs.concurrent.JSExecutionContext.Implicits.runNow

If you prefer on the JVM to use the global execution context, which is backed by a thread pool, instead of ScalaTest's default serial execution contex, which confines execution to a single thread, you would write:

// on the JVM (and also compiles on Scala.js, giving
// you the queue execution context)
implicit override def executionContext =
    scala.concurrent.ExecutionContext.Implicits.global

Serial and parallel test execution

By default (unless you mix in ParallelTestExecution), tests in an AsyncWordSpec will be executed one after another, i.e., serially. This is true whether those tests return Assertion or Future[Assertion], no matter what threads are involved. This default behavior allows you to re-use a shared fixture, such as an external database that needs to be cleaned after each test, in multiple tests in async-style suites. This is implemented by registering each test, other than the first test, to run as a continuation after the previous test completes.

If you want the tests of an AsyncWordSpec to be executed in parallel, you must mix in ParallelTestExecution and enable parallel execution of tests in your build. You enable parallel execution in Runner with the -P command line flag. In the ScalaTest Maven Plugin, set parallel to true. In sbt, parallel execution is the default, but to be explicit you can write:

parallelExecution in Test := true // the default in sbt

On the JVM, if both ParallelTestExecution is mixed in and parallel execution is enabled in the build, tests in an async-style suite will be started in parallel, using threads from the Distributor, and allowed to complete in parallel, using threads from the executionContext. If you are using ScalaTest's serial execution context, the JVM default, asynchronous tests will run in parallel very much like traditional (such as WordSpec) tests run in parallel: 1) Because ParallelTestExecution extends OneInstancePerTest, each test will run in its own instance of the test class, you need not worry about synchronizing access to mutable instance state shared by different tests in the same suite. 2) Because the serial execution context will confine the execution of each test to the single thread that executes the test body, you need not worry about synchronizing access to shared mutable state accessed by transformations and callbacks of Futures inside the test.

If ParallelTestExecution is mixed in but parallel execution of suites is not enabled, asynchronous tests on the JVM will be started sequentially, by the single thread that invoked run, but without waiting for one test to complete before the next test is started. As a result, asynchronous tests will be allowed to complete in parallel, using threads from the executionContext. If you are using the serial execution context, however, you'll see the same behavior you see when parallel execution is disabled and a traditional suite that mixes in ParallelTestExecution is executed: the tests will run sequentially. If you use an execution context backed by a thread-pool, such as global, however, even though tests will be started sequentially by one thread, they will be allowed to run concurrently using threads from the execution context's thread pool.

The latter behavior is essentially what you'll see on Scala.js when you execute a suite that mixes in ParallelTestExecution. Because only one thread exists when running under JavaScript, you can't "enable parallel execution of suites." However, it may still be useful to run tests in parallel on Scala.js, because tests can invoke API calls that are truly asynchronous by calling into external APIs that take advantage of non-JavaScript threads. Thus on Scala.js, ParallelTestExecution allows asynchronous tests to run in parallel, even though they must be started sequentially. This may give you better performance when you are using API calls in your Scala.js tests that are truly asynchronous.

Futures and expected exceptions

If you need to test for expected exceptions in the context of futures, you can use the recoverToSucceededIf and recoverToExceptionIf methods of trait RecoverMethods. Because this trait is mixed into supertrait AsyncTestSuite, both of these methods are available by default in an AsyncWordSpec.

If you just want to ensure that a future fails with a particular exception type, and do not need to inspect the exception further, use recoverToSucceededIf:

recoverToSucceededIf[IllegalStateException] { // Result type: Future[Assertion]
  emptyStackActor ? Peek
}

The recoverToSucceededIf method performs a job similar to assertThrows, except in the context of a future. It transforms a Future of any type into a Future[Assertion] that succeeds only if the original future fails with the specified exception. Here's an example in the REPL:

scala> import org.scalatest.RecoverMethods._
import org.scalatest.RecoverMethods._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.ExecutionContext.Implicits.global

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new IllegalStateException }
     | }
res0: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res0.value
res1: Option[scala.util.Try[org.scalatest.Assertion]] = Some(Success(Succeeded))

Otherwise it fails with an error message similar to those given by assertThrows:

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new RuntimeException }
     | }
res2: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res2.value
res3: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but java.lang.RuntimeException
      was thrown))

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { 42 }
     | }
res4: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res4.value
res5: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but no exception was thrown))

The recoverToExceptionIf method differs from the recoverToSucceededIf in its behavior when the assertion succeeds: recoverToSucceededIf yields a Future[Assertion], whereas recoverToExceptionIf yields a Future[T], where T is the expected exception type.

recoverToExceptionIf[IllegalStateException] { // Result type: Future[IllegalStateException]
  emptyStackActor ? Peek
}

In other words, recoverToExpectionIf is to intercept as recovertToSucceededIf is to assertThrows. The first one allows you to perform further assertions on the expected exception. The second one gives you a result type that will satisfy the type checker at the end of the test body. Here's an example showing recoverToExceptionIf in the REPL:

scala> val futureEx =
     |   recoverToExceptionIf[IllegalStateException] {
     |     Future { throw new IllegalStateException("hello") }
     |   }
futureEx: scala.concurrent.Future[IllegalStateException] = ...

scala> futureEx.value
res6: Option[scala.util.Try[IllegalStateException]] =
    Some(Success(java.lang.IllegalStateException: hello))

scala> futureEx map { ex => assert(ex.getMessage == "world") }
res7: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res7.value
res8: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: "[hello]" did not equal "[world]"))

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, AsyncWordSpec adds a method ignore to strings that can be used instead of in to register a test. For example, to temporarily disable the test with the name "A Stack should pop values in last-in-first-out order", just change “in” into “ignore,” like this:

package org.scalatest.examples.asyncwordspec.ignore

import org.scalatest.AsyncWordSpec
import scala.concurrent.Future

class AddSpec extends AsyncWordSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" should {
    "eventually compute a sum of passed Ints" ignore {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" should {
    "immediately compute a sum of passed Ints" in {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

If you run this version of AddSpec with:

scala> org.scalatest.run(new AddSpec)

It will run only the second test and report that the first test was ignored:

AddSpec:
addSoon
- should eventually compute a sum of passed Ints !!! IGNORED !!!
addNow
- should immediately compute a sum of passed Ints

If you wish to temporarily ignore an entire suite of tests, you can (on the JVM, not Scala.js) annotate the test class with @Ignore, like this:

package org.scalatest.examples.asyncwordspec.ignoreall

import org.scalatest.AsyncWordSpec
import scala.concurrent.Future
import org.scalatest.Ignore

@Ignore
class AddSpec extends AsyncWordSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" should {
    "eventually compute a sum of passed Ints" in {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" should {
    "immediately compute a sum of passed Ints" in {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the AddSpec in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above AddSpec in the Scala interpreter, you'll see:

AddSpec:
addSoon
- should eventually compute a sum of passed Ints !!! IGNORED !!!
addNow
- should immediately compute a sum of passed Ints !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class visible, to encourage the developers to eventually fix and “un-ignore” it. If you want to prevent a class from being discovered at all (on the JVM, not Scala.js), use the DoNotDiscover annotation instead.

If you want to ignore all tests of a suite on Scala.js, where annotations can't be inspected at runtime, you'll need to change it to ignore at each test site. To make a suite non-discoverable on Scala.js, ensure it does not declare a public no-arg constructor. You can either declare a public constructor that takes one or more arguments, or make the no-arg constructor non-public. Because this technique will also make the suite non-discoverable on the JVM, it is a good approach for suites you want to run (but not be discoverable) on both Scala.js and the JVM.

Informers

One of the parameters to AsyncWordSpec's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the reporting done by default by AsyncWordSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event.

One use case for the Informer is to pass more information about a specification to the reporter. For example, the GivenWhenThen trait provides methods that use the implicit info provided by AsyncWordSpec to pass such information to the reporter. Here's an example:

package org.scalatest.examples.asyncwordspec.info

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncWordSpec with GivenWhenThen {

  "A mutable Set" should {
    "allow an element to be added" in {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      info("That's all folks!")
      succeed
    }
  }
}

If you run this AsyncWordSpec from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSpec)
A mutable Set
- should allow an element to be added
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

Documenters

AsyncWordSpec also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example AsyncWordSpec that uses markup:

package org.scalatest.examples.asyncwordspec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncWordSpec with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

    def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  "A mutable Set" should {
    "allow an element to be added" in {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      markup("This test finished with a **bold** statement!")
      succeed
    }
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.asyncwordspec.note

import collection.mutable
import org.scalatest._

class SetSpec extends AsyncWordSpec {

  "A mutable Set" should {
    "allow an element to be added" in {

      info("info is recorded")
      markup("markup is *also* recorded")
      note("notes are sent immediately")
      alert("alerts are also sent immediately")

      val set = mutable.Set.empty[String]
      set += "clarity"
      assert(set.size === 1)
      assert(set.contains("clarity"))
    }
  }
}

Because note and alert information is sent immediately, it will appear before the test name in string reporters, and its color will be unrelated to the ultimate outcome of the test: note text will always appear in green, alert text will always appear in yellow. Here's an example:

scala> org.scalatest.run(new SetSpec)
SetSpec:
A mutable Set
  + notes are sent immediately
  + alerts are also sent immediately
- should allow an element to be added
  + info is recorded
  + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality, has not yet been implemented. Here's an example:

package org.scalatest.examples.asyncwordspec.pending

import org.scalatest.AsyncWordSpec
import scala.concurrent.Future

class AddSpec extends AsyncWordSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" should {
    "eventually compute a sum of passed Ints" in (pending)
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" should {
    "immediately compute a sum of passed Ints" in {
      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

(Note: "(pending)" is the body of the test. Thus the test contains just one statement, an invocation of the pending method, which throws TestPendingException.) If you run this version of AddSpec with:

scala> org.scalatest.run(new AddSpec)

It will run both tests, but report that first test is pending. You'll see:

AddSpec:
addSoon
- should eventually compute a sum of passed Ints (pending)
addNow
- should immediately compute a sum of passed Ints

One difference between an ignored test and a pending one is that an ignored test is intended to be used during significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException.

Tagging tests

An AsyncFunSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing an AsyncFunSpec, groups of tests can optionally be included and/or excluded. To tag an AsyncFunSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for AsyncFunSpecs like this:

package org.scalatest.examples.asyncwordspec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place AsyncFunSpec tests into groups with tags like this:

import org.scalatest.AsyncWordSpec
import org.scalatest.tagobjects.Slow
import scala.concurrent.Future

class AddSpec extends AsyncWordSpec {

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "addSoon" should {
    "eventually compute a sum of passed Ints" taggedAs(Slow) in {
      val futureSum: Future[Int] = addSoon(1, 2)
      // You can map assertions onto a Future, then return
      // the resulting Future[Assertion] to ScalaTest:
      futureSum map { sum => assert(sum == 3) }
    }
  }

  def addNow(addends: Int*): Int = addends.sum

  "addNow" should {
    "immediately compute a sum of passed Ints" taggedAs(Slow, DbTest) in {

      val sum: Int = addNow(1, 2)
      // You can also write synchronous tests. The body
      // must have result type Assertion:
      assert(sum == 3)
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of an AsyncFunSpec in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication in async styles:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and eliminate the need to synchronize access to shared mutable state on the JVM.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgAsyncTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgAsyncTest)` instead)
`withFixture(OneArgAsyncTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or a holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.asyncwordspec.getfixture

import org.scalatest.AsyncWordSpec
import scala.concurrent.Future

class ExampleSpec extends AsyncWordSpec {

  def fixture: Future[String] = Future { "ScalaTest is " }

  "Testing" should {
    "be easy" in {
      val future = fixture
      val result = future map { s => s + "easy!" }
      result map { s =>
        assert(s == "ScalaTest is easy!")
      }
    }

    "be fun" in {
      val future = fixture
      val result = future map { s => s + "fun!" }
      result map { s =>
        assert(s == "ScalaTest is fun!")
      }
    }
  }
}

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, you could pass in an initial value for a fixture object as a parameter to the get-fixture method.

Overriding `withFixture(NoArgAsyncTest)`

Although the get-fixture method approach takes care of setting up a fixture at the beginning of each test, it doesn't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgAsyncTest), a method defined in trait AsyncTestSuite, a supertrait of AsyncFunSpec.

Trait AsyncFunSpec's runTest method passes a no-arg async test function to withFixture(NoArgAsyncTest). It is withFixture's responsibility to invoke that test function. The default implementation of withFixture simply invokes the function and returns the result, like this:

// Default implementation in trait AsyncTestSuite
protected def withFixture(test: NoArgAsyncTest): FutureOutcome = {
  test()
}

You can, therefore, override withFixture to perform setup before invoking the test function, and/or perform cleanup after the test completes. The recommended way to ensure cleanup is performed after a test completes is to use the complete-lastly syntax, defined in supertrait CompleteLastly. The complete-lastly syntax will ensure that cleanup will occur whether future-producing code completes abruptly by throwing an exception, or returns normally yielding a future. In the latter case, complete-lastly will register the cleanup code to execute asynchronously when the future completes.

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. In other words, instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  complete {
    super.withFixture(test) // Invoke the test function
  } lastly {
    // Perform cleanup here
  }
}

If you have no cleanup to perform, you can write withFixture like this instead:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  super.withFixture(test) // Invoke the test function
}

If you want to perform an action only for certain outcomes, you'll need to register code performing that action as a callback on the Future using one of Future's registration methods: onComplete, onSuccess, or onFailure. Note that if a test fails, that will be treated as a scala.util.Success(org.scalatest.Failed). So if you want to perform an action if a test fails, for example, you'd register the callback using onSuccess.

Here's an example in which withFixture(NoArgAsyncTest) is used to take a snapshot of the working directory if a test fails, and send that information to the standard output stream:

package org.scalatest.examples.asyncwordspec.noargasynctest

import java.io.File
import org.scalatest._
import scala.concurrent.Future

class ExampleSpec extends AsyncWordSpec {

  override def withFixture(test: NoArgAsyncTest) = {

    super.withFixture(test) onFailedThen { _ =>
      val currDir = new File(".")
      val fileNames = currDir.list()
      info("Dir snapshot: " + fileNames.mkString(", "))
    }
  }

  def addSoon(addends: Int*): Future[Int] = Future { addends.sum }

  "This test" should {
    "succeed" in {
      addSoon(1, 1) map { sum => assert(sum == 2) }
    }

    "fail" in {
      addSoon(1, 1) map { sum => assert(sum == 3) }
    }
  }
}

Running this version of ExampleSpec in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSpec)
ExampleSpec:
This test
- should succeed
- should fail *** FAILED ***
  2 did not equal 3 (:33)

Note that the NoArgAsyncTest passed to withFixture, in addition to an apply method that executes the test, also includes the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Lastly, if you want to transform the outcome in some way in withFixture, you'll need to use either the map or transform methods of Future, like this:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  val futureOutcome = super.withFixture(test) // Invoke the test function

  futureOutcome change { outcome =>
    // transform the outcome into a new outcome here
  }
}

Note that a NoArgAsyncTest's apply method will return a scala.util.Failure only if the test completes abruptly with a "test-fatal" exception (such as OutOfMemoryError) that should cause the suite to abort rather than the test to fail. Thus usually you would use map to transform future outcomes, not transform, so that such test-fatal exceptions pass through unchanged. The suite will abort asynchronously with any exception returned from NoArgAsyncTest's apply method in a scala.util.Failure.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

package org.scalatest.examples.asyncwordspec.loanfixture

import java.util.concurrent.ConcurrentHashMap

import scala.concurrent.Future
import scala.concurrent.ExecutionContext

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private final val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer // java.lang.StringBuffer is thread-safe
    databases.put(name, db)
    db
  }
  def removeDb(name: String): Unit = {
    databases.remove(name)
  }
}

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

import org.scalatest._
import DbServer._
import java.util.UUID.randomUUID

class ExampleSpec extends AsyncWordSpec {

  def withDatabase(testCode: Future[Db] => Future[Assertion]) = {
    val dbName = randomUUID.toString // generate a unique db name
    val futureDb = Future { createDb(dbName) } // create the fixture
    complete {
      val futurePopulatedDb =
        futureDb map { db =>
          db.append("ScalaTest is ") // perform setup
        }
      testCode(futurePopulatedDb) // "loan" the fixture to the test code
    } lastly {
      removeDb(dbName) // ensure the fixture will be cleaned up
    }
  }

  def withActor(testCode: StringActor => Future[Assertion]) = {
    val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is ") // set up the fixture
      testCode(actor) // "loan" the fixture to the test code
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  "Testing" should {
    // This test needs the actor fixture
    "be productive" in {
      withActor { actor =>
        actor ! Append("productive!")
        val futureString = actor ? GetValue
        futureString map { s =>
          assert(s == "ScalaTest is productive!")
        }
      }
    }
  }

  "Test code" should {
    // This test needs the database fixture
    "be readable" in {
      withDatabase { futureDb =>
        futureDb map { db =>
          db.append("readable!")
          assert(db.toString == "ScalaTest is readable!")
        }
      }
    }

    // This test needs both the actor and the database
    "be clear and concise" in {
      withDatabase { futureDb =>
        withActor { actor => // loan-fixture methods compose
          actor ! Append("concise!")
          val futureString = actor ? GetValue
          val futurePair: Future[(Db, String)] =
            futureDb zip futureString
          futurePair map { case (db, s) =>
            db.append("clear!")
            assert(db.toString == "ScalaTest is clear!")
            assert(s == "ScalaTest is concise!")
          }
        }
      }
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating databases, it is a good idea to give each database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.AsyncTestSuite and overriding withFixture(OneArgAsyncTest). Each test in a fixture.AsyncTestSuite takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgAsyncTest. This withFixture method is responsible for invoking the one-arg async test function, so you can perform fixture set up before invoking and passing the fixture into the test function, and ensure clean up is performed after the test completes.

To enable the stacking of traits that define withFixture(NoArgAsyncTest), it is a good idea to let withFixture(NoArgAsyncTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgAsyncTest to a NoArgAsyncTest. You can do that by passing the fixture object to the toNoArgAsyncTest method of OneArgAsyncTest. In other words, instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgAsyncTest) method of the same instance by writing:

withFixture(test.toNoArgAsyncTest(theFixture))

Here's a complete example:

package org.scalatest.examples.asyncwordspec.oneargasynctest

import org.scalatest._
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSpec extends fixture.AsyncWordSpec {

  type FixtureParam = StringActor

  def withFixture(test: OneArgAsyncTest): FutureOutcome = {

    val actor = new StringActor
    complete {
      actor ! Append("ScalaTest is ") // set up the fixture
      withFixture(test.toNoArgAsyncTest(actor))
    } lastly {
      actor ! Clear // ensure the fixture will be cleaned up
    }
  }

  "Testing" should {
    "be easy" in { actor =>
      actor ! Append("easy!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is easy!")
      }
    }

    "be fun" in { actor =>
      actor ! Append("fun!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is fun!")
      }
    }
  }
}

In this example, the tests required one fixture object, a StringActor. If your tests need multiple fixture objects, you can simply define the FixtureParam type to be a tuple containing the objects or, alternatively, a case class containing the objects. For more information on the withFixture(OneArgAsyncTest) technique, see the documentation for fixture.AsyncFunSpec.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.asyncwordspec.beforeandafter

import org.scalatest.AsyncWordSpec
import org.scalatest.BeforeAndAfter
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class ExampleSpec extends AsyncWordSpec with BeforeAndAfter {

  final val actor = new StringActor

  before {
    actor ! Append("ScalaTest is ") // set up the fixture
  }

  after {
    actor ! Clear // clean up the fixture
  }

  "Testing" should {
    "be easy" in {
      actor ! Append("easy!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is easy!")
      }
    }

    "be fun" in {
      actor ! Append("fun!")
      val futureString = actor ? GetValue
      futureString map { s =>
        assert(s == "ScalaTest is fun!")
      }
    }
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state.

Note that on the JVM, if you override ScalaTest's default serial execution context, you will likely need to worry about synchronizing access to shared mutable fixture state, because the execution context may assign different threads to process different Future transformations. Although access to mutable state along the same linear chain of Future transformations need not be synchronized, it can be difficult to spot cases where these constraints are violated. The best approach is to use only immutable objects when transforming Futures. When that's not practical, involve only thread-safe mutable objects, as is done in the above example. On Scala.js, by contrast, you need not worry about thread synchronization, because in effect only one thread exists.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilderActor and StringBufferActor fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.asyncwordspec.composingwithasyncfixture

import org.scalatest._
import org.scalatest.SuiteMixin
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val builderActor = new StringBuilderActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    builderActor ! Append("ScalaTest is ")
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      builderActor ! Clear
    }
  }
}

trait Buffer extends AsyncTestSuiteMixin { this: AsyncTestSuite =>

  final val bufferActor = new StringBufferActor

  abstract override def withFixture(test: NoArgAsyncTest) = {
    complete {
      super.withFixture(test) // To be stackable, must call super.withFixture
    } lastly {
      bufferActor ! Clear
    }
  }
}

class ExampleSpec extends AsyncWordSpec with Builder with Buffer {

  "Testing" should {
    "be easy" in {
      builderActor ! Append("easy!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is easy!")
        assert(lst.isEmpty)
        bufferActor ! Append("sweet")
        succeed
      }
    }

    "be fun" in {
      builderActor ! Append("fun!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is fun!")
        assert(lst.isEmpty)
        bufferActor ! Append("awesome")
        succeed
      }
    }
  }
}

By mixing in both the Builder and Buffer traits, ExampleSpec gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Spec extends AsyncWordSpec with Buffer with Builder

If you only need one fixture you mix in only that trait:

class Example3Spec extends AsyncWordSpec with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.asyncwordspec.composingbeforeandaftereach

import org.scalatest._
import org.scalatest.BeforeAndAfterEach
import collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Defining actor messages
sealed abstract class StringOp
case object Clear extends StringOp
case class Append(value: String) extends StringOp
case object GetValue

class StringBuilderActor { // Simulating an actor
  private final val sb = new StringBuilder
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => sb.append(value)
        case Clear => sb.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[String] =
    Future {
      synchronized { sb.toString }
    }
}

class StringBufferActor {
  private final val buf = ListBuffer.empty[String]
  def !(op: StringOp): Unit =
    synchronized {
      op match {
        case Append(value) => buf += value
        case Clear => buf.clear()
      }
    }
  def ?(get: GetValue.type)(implicit c: ExecutionContext): Future[List[String]] =
    Future {
      synchronized { buf.toList }
    }
}

trait Builder extends BeforeAndAfterEach { this: Suite =>

  final val builderActor = new StringBuilderActor

  override def beforeEach() {
    builderActor ! Append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builderActor ! Clear
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  final val bufferActor = new StringBufferActor

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally bufferActor ! Clear
  }
}

class ExampleSpec extends AsyncWordSpec with Builder with Buffer {

  "Testing" should {

    "be easy" in {
      builderActor ! Append("easy!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is easy!")
        assert(lst.isEmpty)
        bufferActor ! Append("sweet")
        succeed
      }
    }

    "be fun" in {
      builderActor ! Append("fun!")
      val futureString = builderActor ? GetValue
      val futureList = bufferActor ? GetValue
      val futurePair: Future[(String, List[String])] = futureString zip futureList
      futurePair map { case (str, lst) =>
        assert(str == "ScalaTest is fun!")
        assert(lst.isEmpty)
        bufferActor ! Append("awesome")
        succeed
      }
    }
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in an AsyncFunSpec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any AsyncFunSpec that uses them, so that the tests they contain will be registered as tests in that AsyncFunSpec. For example, given this StackActor class:

package org.scalatest.examples.asyncwordspec.sharedtests

import scala.collection.mutable.ListBuffer
import scala.concurrent.Future
import scala.concurrent.ExecutionContext

// Stack operations
case class Push[T](value: T)
sealed abstract class StackOp
case object Pop extends StackOp
case object Peek extends StackOp
case object Size extends StackOp

// Stack info
case class StackInfo[T](top: Option[T], size: Int, max: Int) {
  require(size > 0, "size was less than zero")
  require(max > size, "max was less than size")
  val isFull: Boolean = size == max
  val isEmpty: Boolean = size == 0
}

class StackActor[T](Max: Int, name: String) {

  private final val buf = new ListBuffer[T]

  def !(push: Push[T]): Unit =
    synchronized {
      if (buf.size != Max)
        buf.prepend(push.value)
      else
        throw new IllegalStateException("can't push onto a full stack")
    }

  def ?(op: StackOp)(implicit c: ExecutionContext): Future[StackInfo[T]] =
    synchronized {
      op match {
        case Pop =>
          Future {
            if (buf.size != 0)
              StackInfo(Some(buf.remove(0)), buf.size, Max)
            else
              throw new IllegalStateException("can't pop an empty stack")
          }
        case Peek =>
          Future {
            if (buf.size != 0)
              StackInfo(Some(buf(0)), buf.size, Max)
            else
              throw new IllegalStateException("can't peek an empty stack")
          }
        case Size =>
          Future { StackInfo(None, buf.size, Max) }
      }
    }

  override def toString: String = name
}

You may want to test the stack represented by the StackActor class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several tests that make sense any time the stack is non-empty. Thus you'd ideally want to run those same tests for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these tests out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your AsyncFunSpec for StackActor, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared tests are run for all three fixtures.

You can define a behavior function that encapsulates these shared tests inside the AsyncWordSpec that uses them. If they are shared between different AsyncFunSpecs, however, you could also define them in a separate trait that is mixed into each AsyncFunSpec that uses them. For example, here the nonEmptyStackActor behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared tests for non-full stacks:

import org.scalatest.AsyncWordSpec

trait AsyncWordSpecStackBehaviors { this: AsyncWordSpec =>

  def nonEmptyStackActor(createNonEmptyStackActor: => StackActor[Int],
        lastItemAdded: Int, name: String): Unit = {

    ("return non-empty StackInfo when Size is fired at non-empty stack actor: " + name) in {
      val stackActor = createNonEmptyStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isEmpty)
      }
    }

    ("return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: " + name) in {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePeek <- stackActor ? Size
          afterPeek <- stackActor ? Peek
        } yield (beforePeek, afterPeek)
      futurePair map { case (beforePeek, afterPeek) =>
        assert(afterPeek.top == Some(lastItemAdded))
        assert(afterPeek.size == beforePeek.size)
      }
    }

    ("return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: " + name) in {
      val stackActor = createNonEmptyStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePop <- stackActor ? Size
          afterPop <- stackActor ? Pop
        } yield (beforePop, afterPop)
      futurePair map { case (beforePop, afterPop) =>
        assert(afterPop.top == Some(lastItemAdded))
        assert(afterPop.size == beforePop.size - 1)
      }
    }
  }

  def nonFullStackActor(createNonFullStackActor: => StackActor[Int], name: String): Unit = {

    ("return non-full StackInfo when Size is fired at non-full stack actor: " + name) in {
      val stackActor = createNonFullStackActor
      val futureStackInfo = stackActor ? Size
      futureStackInfo map { stackInfo =>
        assert(!stackInfo.isFull)
      }
    }

    ("return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: " + name) in {
      val stackActor = createNonFullStackActor
      val futurePair: Future[(StackInfo[Int], StackInfo[Int])] =
        for {
          beforePush <- stackActor ? Size
          afterPush <- { stackActor ! Push(7); stackActor ? Peek }
        } yield (beforePush, afterPush)
      futurePair map { case (beforePush, afterPush) =>
        assert(afterPush.top == Some(7))
        assert(afterPush.size == beforePush.size + 1)
      }
    }
  }
}

Given these behavior functions, you could invoke them directly, but AsyncWordSpec offers a DSL for the purpose, which looks like this:

behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)
behave like nonFullStackActor(almostEmptyStackActor, almostEmptyStackActorName)

Here's an example:

class StackSpec extends AsyncWordSpec with AsyncWordSpecStackBehaviors {

  val Max = 10
  val LastValuePushed = Max - 1

  // Stack fixture creation methods
  val emptyStackActorName = "empty stack actor"
  def emptyStackActor = new StackActor[Int](Max, emptyStackActorName )

  val fullStackActorName = "full stack actor"
  def fullStackActor = {
    val stackActor = new StackActor[Int](Max, fullStackActorName )
    for (i <- 0 until Max)
      stackActor ! Push(i)
    stackActor
  }

  val almostEmptyStackActorName = "almost empty stack actor"
  def almostEmptyStackActor = {
    val stackActor = new StackActor[Int](Max, almostEmptyStackActorName )
    stackActor ! Push(LastValuePushed)
    stackActor
  }

  val almostFullStackActorName = "almost full stack actor"
  def almostFullStackActor = {
    val stackActor = new StackActor[Int](Max, almostFullStackActorName)
    for (i <- 1 to LastValuePushed)
      stackActor ! Push(i)
    stackActor
  }

  "A Stack" when {
    "empty" should {
      "be empty" in {
        val stackActor = emptyStackActor
        val futureStackInfo = stackActor ? Size
        futureStackInfo map { stackInfo =>
          assert(stackInfo.isEmpty)
        }
      }

      "complain on peek" in {
        recoverToSucceededIf[IllegalStateException] {
          emptyStackActor ? Peek
        }
      }

      "complain on pop" in {
        recoverToSucceededIf[IllegalStateException] {
          emptyStackActor ? Pop
        }
      }
    }
    "non-empty" should {
      behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)
      behave like nonFullStackActor(almostEmptyStackActor, almostEmptyStackActorName)
      behave like nonEmptyStackActor(almostFullStackActor, LastValuePushed, almostFullStackActorName)
      behave like nonFullStackActor(almostFullStackActor, almostFullStackActorName)
    }
    "full" should {
      "be full" in {
        val stackActor = fullStackActor
        val futureStackInfo = stackActor ? Size
        futureStackInfo map { stackInfo =>
          assert(stackInfo.isFull)
        }
      }
      behave like nonEmptyStackActor(fullStackActor, LastValuePushed, fullStackActorName)
      "complain on a push" in {
        val stackActor = fullStackActor
        assertThrows[IllegalStateException] {
          stackActor ! Push(10)
        }
      }
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> org.scalatest.run(new StackSpec)
StackSpec:
A Stack
  when empty
  - should be empty
  - should complain on peek
  - should complain on pop
  when non-empty
  - should return non-empty StackInfo when Size is fired at non-empty stack actor: almost empty stack actor
  - should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost empty stack actor
  - should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost empty stack actor
  - should return non-full StackInfo when Size is fired at non-full stack actor: almost empty stack actor
  - should return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: almost empty stack actor
  - should return non-empty StackInfo when Size is fired at non-empty stack actor: almost full stack actor
  - should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost full stack actor
  - should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost full stack actor
  - should return non-full StackInfo when Size is fired at non-full stack actor: almost full stack actor
  - should return before and after StackInfo that has existing size + 1 and new item as top when Push is fired at non-full stack actor: almost full stack actor
  when full
  - should be full
  - should return non-empty StackInfo when Size is fired at non-empty stack actor: full stack actor
  - should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: full stack actor
  - should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: full stack actor
  - should complain on a push

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. Although in an AsyncWordSpec, the when, should, can and must clause is a nesting construct analogous to AsyncFunSpec's describe clause, you many sometimes need to do a bit of extra work to ensure that the test names are unique. If a duplicate test name problem shows up in an AsyncFunSpec, you'll need to pass in a prefix or suffix string to add to each test name. You can call toString on the shared fixture object, or pass this string the same way you pass any other data needed by the shared tests. This is the approach taken by the previous AsyncFunSpecStackBehaviors example.

Given this AsyncFunSpecStackBehaviors trait, calling it with the almostEmptyStackActor fixture, like this:

behave like nonEmptyStackActor(almostEmptyStackActor, LastValuePushed, almostEmptyStackActorName)

yields test names:

A Stack when non-empty should return non-empty StackInfo when Size is fired at non-empty stack actor: almost empty stack actor
A Stack when non-empty should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost empty stack actor
A Stack when non-empty should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost empty stack actor

Whereas calling it with the almostFullStackActor fixture, like this:

behave like nonEmptyStackActor(almostFullStackActor, LastValuePushed, almostFullStackActorName)

yields different test names:

A Stack when non-empty should return non-empty StackInfo when Size is fired at non-empty stack actor: almost full stack actor
A Stack when non-empty should return before and after StackInfo that has existing size and lastItemAdded as top when Peek is fired at non-empty stack actor: almost full stack actor
A Stack when non-empty should return before and after StackInfo that has existing size - 1 and lastItemAdded as top when Pop is fired at non-empty stack actor: almost full stack actor

trait AsyncWordSpecLike extends AsyncTestSuite with AsyncTestRegistration with ShouldVerb with MustVerb with CanVerb with Informing with Notifying with Alerting with Documenting

Implementation trait for class AsyncWordSpec, which facilitates a “behavior-driven” style of development (BDD), in which tests are combined with text that specifies the behavior the tests verify.

AsyncWordSpec is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of AsyncWordSpec into some other class, you can use this trait instead, because class AsyncWordSpec does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of AsyncWordSpec.

trait BeforeAndAfter extends SuiteMixin

Trait that can be mixed into suites that need code executed before and after running each test.

Recommended Usage: Use trait BeforeAndAfter when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests. Note: For more insight into where BeforeAndAfter fits into the big picture, see the Shared fixtures section in the documentation for your chosen style trait.

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code. Trait BeforeAndAfter offers one way to eliminate such code duplication: a before clause that will register code to be run before each test, and an after clause that will register code to be run after.

Here's an example:

package org.scalatest.examples.flatspec.beforeandafter

import org.scalatest._
import collection.mutable.ListBuffer

class ExampleSpec extends FlatSpec with BeforeAndAfter {

  val builder = new StringBuilder
  val buffer = new ListBuffer[String]

  before {
    builder.append("ScalaTest is ")
  }

  after {
    builder.clear()
    buffer.clear()
  }

  "Testing" should "be easy" in {
    builder.append("easy!")
    assert(builder.toString === "ScalaTest is easy!")
    assert(buffer.isEmpty)
    buffer += "sweet"
  }

  it should "be fun" in {
    builder.append("fun!")
    assert(builder.toString === "ScalaTest is fun!")
    assert(buffer.isEmpty)
  }
}

The before and after methods can each only be called once per Suite, and cannot be invoked after run has been invoked. If either of the registered before or after functions complete abruptly with an exception, it will be reported as an aborted suite and no more tests will be attempted in that suite.

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class unless you synchronized access to the shared, mutable state. This is why ScalaTest's ParallelTestExecution trait extends OneInstancePerTest. By running each test in its own instance of the class, each test has its own copy of the instance variables, so you don't need to synchronize. Were you to mix ParallelTestExecution into the ExampleSuite above, the tests would run in parallel just fine without any synchronization needed on the mutable StringBuilder and ListBuffer[String] objects.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead.

The advantage this trait has over BeforeAndAfterEach is that its syntax is more concise. The main disadvantage is that it is not stackable, whereas BeforeAndAfterEach is. I.e., you can write several traits that extend BeforeAndAfterEach and provide beforeEach methods that include a call to super.beforeEach, and mix them together in various combinations. By contrast, only one call to the before registration function is allowed in a suite or spec that mixes in BeforeAndAfter. In addition, BeforeAndAfterEach allows you to access the config map and test name via the TestData passed to its beforeEach and afterEach methods, whereas BeforeAndAfter gives you no access to the config map.

trait BeforeAndAfterAll extends SuiteMixin

Stackable trait that can be mixed into suites that need methods invoked before and after executing the suite.

This trait allows code to be executed before and/or after all the tests and nested suites of a suite are run. This trait overrides run and calls the beforeAll method, then calls super.run. After the super.run invocation completes, whether it returns normally or completes abruptly with an exception, this trait's run method will invoke afterAll.

Trait BeforeAndAfterAll defines beforeAll and afterAll methods that take no parameters. This trait's implementation of these methods do nothing.

For example, the following ExampleSpec mixes in BeforeAndAfterAll and in beforeAll, creates and writes to a temp file. Each test class, ExampleSpec and all its nested suites--OneSpec, TwoSpec, RedSpec, and BlueSpec--tests that the file exists. After all of the nested suites have executed, afterAll is invoked, which deletes the file. (Note: if you're unfamiliar with the withFixture(OneArgTest) approach to shared fixtures, check out the documentation for trait fixture.FlatSpec.)

package org.scalatest.examples.beforeandafterall

import org.scalatest._
import java.io._

trait TempFileExistsSpec extends fixture.FlatSpecLike {

  protected val tempFileName = "tmp.txt"

  type FixtureParam = File
  override def withFixture(test: OneArgTest) = {
    val file = new File(tempFileName)
    withFixture(test.toNoArgTest(file)) // loan the fixture to the test
  }

  "The temp file" should ("exist in " + suiteName) in { file =>
    assert(file.exists)
  }
}

class OneSpec extends TempFileExistsSpec
class TwoSpec extends TempFileExistsSpec
class RedSpec extends TempFileExistsSpec
class BlueSpec extends TempFileExistsSpec

class ExampleSpec extends Suites(
  new OneSpec,
  new TwoSpec,
  new RedSpec,
  new BlueSpec
) with TempFileExistsSpec with BeforeAndAfterAll {

  // Set up the temp file needed by the test, taking
  // a file name from the config map
  override def beforeAll() {
    val writer = new FileWriter(tempFileName)
    try writer.write("Hello, suite of tests!")
    finally writer.close()
  }

  // Delete the temp file
  override def afterAll() {
    val file = new File(tempFileName)
    file.delete()
  }
}

If you do supply a mapping for "tempFileName" in the config map, you'll see that the temp file is available to all the tests:

scala> org.scalatest.run(new ExampleSpec)
ExampleSpec:
OneSpec:
The temp file
- should exist in OneSpec
TwoSpec:
The temp file
- should exist in TwoSpec
RedSpec:
The temp file
- should exist in RedSpec
BlueSpec:
The temp file
- should exist in BlueSpec
The temp file
- should exist in ExampleSpec

Note: this trait uses the Status result of Suite's "run" methods to ensure that the code in afterAll is executed after all the tests and nested suites are executed even if a Distributor is passed.

Note that it is not guaranteed that afterAll is invoked from the same thread as beforeAll, so if there's any shared state between beforeAll and afterAll you'll need to make sure they are synchronized correctly.

trait BeforeAndAfterAllConfigMap extends SuiteMixin

Trait that can be mixed into suites that need methods that make use of the config map invoked before and/or after executing the suite.

This trait allows code to be executed before and/or after all the tests and nested suites of a suite are run. This trait overrides run and calls the beforeAll(ConfigMap) method, then calls super.run. After the super.run invocation completes, whether it returns normally or completes abruptly with an exception, this trait's run method will invoke afterAll(ConfigMap).

Note that this trait differs from BeforeAndAfterAll in that it gives the beforeAll and afterAll code access to the config map. If you don't need the config map, use BeforeAndAfterAll instead.

Trait BeforeAndAfterAllConfigMap defines beforeAll and afterAll methods that take a configMap. This trait's implemention of each method does nothing.

For example, the following ExampleSpec mixes in BeforeAndAfterAllConfigMap and in beforeAll, creates and writes to a temp file, taking the name of the temp file from the configMap. This same configMap is then passed to the run methods of the nested suites, OneSpec, TwoSpec, RedSpec, and BlueSpec, so those suites can access the filename and, therefore, the file's contents. After all of the nested suites have executed, afterAll is invoked, which again grabs the file name from the configMap and deletes the file. Each of these five test classes extend trait TempFileExistsSpec, which defines a test that ensures the temp file exists. (Note: if you're unfamiliar with the withFixture(OneArgTest) approach to shared fixtures, check out the documentation for trait fixture.FlatSpec.)

package org.scalatest.examples.beforeandafterallconfigmap

import org.scalatest._
import java.io._

trait TempFileExistsSpec extends fixture.FlatSpec {

  type FixtureParam = File
  override def withFixture(test: OneArgTest) = {
    val fileName = test.configMap.getRequired[String]("tempFileName")
    val file = new File(fileName)
    withFixture(test.toNoArgTest(file)) // loan the fixture to the test
  }

  "The temp file" should ("exist in " + suiteName) in { file =>
    assert(file.exists)
  }
}

class OneSpec extends TempFileExistsSpec
class TwoSpec extends TempFileExistsSpec
class RedSpec extends TempFileExistsSpec
class BlueSpec extends TempFileExistsSpec

class ExampleSpec extends Suites(
  new OneSpec,
  new TwoSpec,
  new RedSpec,
  new BlueSpec
) with TempFileExistsSpec with BeforeAndAfterAllConfigMap {

  private val tempFileName = "tempFileName"

  // Set up the temp file needed by the test, taking
  // a file name from the config map
  override def beforeAll(cm: ConfigMap) {
    assume(
      cm.isDefinedAt(tempFileName),
      "must place a temp file name in the config map under the key: " + tempFileName
    )
    val fileName = cm.getRequired[String](tempFileName)
    val writer = new FileWriter(fileName)
    try writer.write("Hello, suite of tests!")
    finally writer.close()
  }

  // Delete the temp file
  override def afterAll(cm: ConfigMap) {
    val fileName = cm.getRequired[String]("tempFileName")
    val file = new File(fileName)
    file.delete()
  }
}

Running the above class in the interpreter will give an error if you don't supply a mapping for "tempFileName" in the config map:

scala> org.scalatest.run(new ExampleSpec)
ExampleSpec:
Exception encountered when invoking run on a suite. *** ABORTED ***
  Exception encountered when invoking run on a suite. (:30)
*** RUN ABORTED ***
  An exception or error caused a run to abort: must place a temp file name in the config map under the key: tempFileName (:30)

If you do supply a mapping for "tempFileName" in the config map, you'll see that the temp file is available to all the tests:

scala> (new ExampleSpec).execute(configMap = ConfigMap("tempFileName" -> "tmp.txt"))
ExampleSpec:
OneSpec:
The temp file
- should exist in OneSpec
TwoSpec:
The temp file
- should exist in TwoSpec
RedSpec:
The temp file
- should exist in RedSpec
BlueSpec:
The temp file
- should exist in BlueSpec
The temp file
- should exist in ExampleSpec

Note: As of 2.0.M5, this trait uses the newly added Status result of Suite's "run" methods to ensure that the code in afterAll is executed after all the tests and nested suites are executed even if a Distributor is passed.

Note that it is not guaranteed that afterAll is invoked from the same thread as beforeAll, so if there's any shared state between beforeAll and afterAll you'll need to make sure they are synchronized correctly.

trait BeforeAndAfterEach extends SuiteMixin

Stackable trait that can be mixed into suites that need code executed before and/or after running each test.

Recommended Usage: Use trait BeforeAndAfterEach when you want to stack traits that perform side-effects before and/or after tests, rather than at the beginning or end of tests. Note: For more insight into where BeforeAndAfterEach fits into the big picture, see the Shared fixtures section in the documentation for your chosen style trait.

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code, and the slower your compile will likely be. Trait BeforeAndAfterEach offers one way to eliminate such code duplication: a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown).

Here's an example:

package org.scalatest.examples.flatspec.composingbeforeandaftereach

import org.scalatest._
import collection.mutable.ListBuffer

trait Builder extends BeforeAndAfterEach { this: Suite =>

  val builder = new StringBuilder

  override def beforeEach() {
    builder.append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try {
      super.afterEach() // To be stackable, must call super.afterEach
    }
    finally {
      builder.clear()
    }
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  val buffer = new ListBuffer[String]

  override def afterEach() {
    try {
      super.afterEach() // To be stackable, must call super.afterEach
    }
    finally {
      buffer.clear()
    }
  }
}

class ExampleSpec extends FlatSpec with Builder with Buffer {

  "Testing" should "be easy" in {
    builder.append("easy!")
    assert(builder.toString === "ScalaTest is easy!")
    assert(buffer.isEmpty)
    buffer += "sweet"
  }

  it should "be fun" in {
    builder.append("fun!")
    assert(builder.toString === "ScalaTest is fun!")
    assert(buffer.isEmpty)
    buffer += "clear"
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The main advantage of BeforeAndAfterEach over BeforeAndAfter is that BeforeAndAfterEach. enables trait stacking. The main disadvantage of BeforeAndAfterEach compared to BeforeAndAfter is that BeforeAndAfterEach requires more boilerplate. If you don't need trait stacking, use BeforeAndAfter instead of BeforeAndAfterEach. If you want to make use of test data (the test name, config map, etc.) in your beforeEach or afterEach method, use trait BeforeAndAfterEachTestData instead.

trait BeforeAndAfterEachTestData extends SuiteMixin

Stackable trait that can be mixed into suites that need code that makes use of test data (test name, tags, config map, etc.) executed before and/or after running each test.

Recommended Usage: Use trait BeforeAndAfterEachTestData when you want to stack traits that perform side-effects before and/or after tests, rather than at the beginning or end of tests, when you need access to any test data (such as the config map) in the before and/or after code. Note: For more insight into where BeforeAndAfterEachTestData fits into the big picture, see the Shared fixtures section in the documentation for your chosen style trait.

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code. Trait BeforeAndAfterEachTestData offers one way to eliminate such code duplication: a beforeEach(TestData) method that will be run before each test (like JUnit's setUp), and an afterEach(TestData) method that will be run after (like JUnit's tearDown).

Here's an example:

package org.scalatest.examples.flatspec.composingbeforeandaftereachtestdata

import org.scalatest._
import collection.mutable.ListBuffer

trait Builder extends BeforeAndAfterEachTestData { this: Suite =>

  val builder = new StringBuilder

  override def beforeEach(td: TestData) {
    builder.append(td.name)
    super.beforeEach(td) // To be stackable, must call super.beforeEach(TestData)
  }

  override def afterEach(td: TestData) {
    try {
      super.afterEach(td) // To be stackable, must call super.afterEach(TestData)
    }
    finally {
      builder.clear()
    }
  }
}

trait Buffer extends BeforeAndAfterEachTestData { this: Suite =>

  val buffer = new ListBuffer[String]

  override def afterEach(td: TestData) {
    try {
      super.afterEach(td) // To be stackable, must call super.afterEach(TestData)
    }
    finally {
      buffer.clear()
    }
  }
}

class ExampleSpec extends FlatSpec with Builder with Buffer {

  "Testing" should "be easy" in {
    builder.append("!")
    assert(builder.toString === "Testing should be easy!")
    assert(buffer.isEmpty)
    buffer += "sweet"
  }

  it should "be fun" in {
    builder.append("!")
    assert(builder.toString === "Testing should be fun!")
    assert(buffer.isEmpty)
    buffer += "clear"
  }
}

To get the same ordering as withFixture, place your super.beforeEach(TestData) call at the end of each beforeEach(TestData) method, and the super.afterEach(TestData) call at the beginning of each afterEach(TestData) method, as shown in the previous example. It is a good idea to invoke super.afterEach(TestData) in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach(TestData) throws an exception.

Besides enabling trait stacking, the other main advantage of BeforeAndAfterEachTestData over BeforeAndAfter is that BeforeAndAfterEachTestData allows you to make use of test data (such as the test name and config map) in your before and/or after code, whereas BeforeAndAfter does not.

The main disadvantage of BeforeAndAfterEachTestData compared to BeforeAndAfter and BeforeAndAfterEach is that BeforeAndAfterEachTestData requires more boilerplate. If you don't need trait stacking or access to the test data, use BeforeAndAfter instead of BeforeAndAfterEachTestData. If you need trait stacking, but not access to the TestData, use BeforeAndAfterEach instead.

trait CancelAfterFailure extends TestSuiteMixin

Trait that when mixed into a TestSuite cancels any remaining tests in that TestSuite instance after a test fails.

The intended use case for this trait is if you have a suite of long-running tests that are related such that if one fails, you aren't interested in running the others, you can use this trait to simply cancel any remaining tests, so you need not wait long for them to complete.

Note that this trait only cancels tests in the same TestSuite instance, because it uses a private volatile instance variable as a flag to indicate whether or not a test has failed. If you are running each test in its own instance, therefore, it would not cancel the remaining tests, because they would not see the same flag. For this reason, this trait contains a final implementation of a method defined in OneInstancePerTest, to prevent it from being mixed into any class that also mixes in OneInstancePerTest, including by mixing in ParallelTestExecution or a path trait.

case class Canceled(exception: TestCanceledException) extends Exceptional with Product with Serializable

Outcome for a test that was canceled, containing an exception describing the cause of the cancelation.

trait Checkpoints extends AnyRef

Trait providing class Checkpoint, which enables multiple assertions to be performed within a test, with any failures accumulated and reported together at the end of the test.

Because ScalaTest uses exceptions to signal failed assertions, normally execution of a test will stop as soon as the first failed assertion is encountered. Trait Checkpoints provides an option when you want to continue executing the remainder of the test body, or part of it, even if an assertion has already failed in that test.

To use a Checkpoint (once you've mixed in or imported the members of trait Checkpoints), you first need to create one, like this:

val cp = new Checkpoint

Then give the Checkpoint assertions to execute by passing them (via a by-name parameter) to its apply method, like this:

val (x, y) = (1, 2)
cp { x should be < 0 }
cp { y should be > 9 }

Both of the above assertions will fail, but it won't be reported yet. The Checkpoint will execute them right away, each time its apply method is invoked. But it will catch the TestFailedExceptions and save them, only reporting them later when reportAll is invoked. Thus, at the end of the test, you must call reportAll, like this:

cp.reportAll()

This reportAll invocation will complete abruptly with a TestFailedException whose message includes the message, source file, and line number of each of the checkpointed assertions that previously failed. For example:

1 was not less than 0 (in Checkpoint) at ExampleSpec.scala:12
2 was not greater than 9 (in Checkpoint) at ExampleSpec.scala:13

Make sure you invoke reportAll before the test completes, otherwise any failures that were detected by the Checkpoint will not be reported.

Note that a Checkpoint will catch and record for later reporting (via reportAll) exceptions that mix in StackDepth except for TestCanceledException, TestRegistrationClosedException, NotAllowedException, and DuplicateTestNameException. If a block of code passed to a Checkpoint's apply method completes abruptly with any of the StackDepth exceptions in the previous list, or any non-StackDepth exception, that invocation of the apply method will complete abruptly with the same exception immediately. Unless you put reportAll in a finally clause and handle this case, such an unexpected exception will cause you to lose any information about assertions that failed earlier in the test and were recorded by the Checkpoint.

trait CompleteLastly extends AnyRef

Trait that provides a complete-lastly construct, which ensures cleanup code in lastly is executed whether the code passed to complete completes abruptly with an exception or successfully results in a Future, FutureOutcome, or other type with an implicit Futuristic instance.

This trait is mixed into ScalaTest's async testing styles, to make it easy to ensure cleanup code will execute whether code that produces a "futuristic" value (any type F for which a Futuristic[F] instance is implicitly available). ScalaTest provides implicit Futuristic instances for Future[T] for any type T and FutureOutcome.

If the future-producing code passed to complete throws an exception, the cleanup code passed to lastly will be executed immediately, and the same exception will be rethrown, unless the code passed to lastly also completes abruptly with an exception. In that case, complete-lastly will complete abruptly with the exception thrown by the code passed to lastly (this mimics the behavior of finally).

Otherwise, if the code passed to complete successfully returns a Future (or other "futuristic" type), complete-lastly will register the cleanup code to be performed once the future completes and return a new future that will complete once the original future completes and the subsequent cleanup code has completed execution. The future returned by complete-lastly will have the same result as the original future passed to complete, unless the cleanup code throws an exception. If the cleanup code passed to lastly throws an exception, the future returned by lastly will fail with that exception.

The complete-lastly syntax is intended to be used to ensure cleanup code is executed in async testing styles like try-finally is used in traditional testing styles. Here's an example of complete-lastly used in withFixture in an async testing style:

// Your implementation
override def withFixture(test: NoArgAsyncTest) = {

  // Perform setup here

  complete {
    super.withFixture(test) // Invoke the test function
  } lastly {
    // Perform cleanup here
  }
}

final class CompositeStatus extends Status with Serializable

Composite Status that aggregates its completion and failed states of set of other Statuses passed to its constructor.

class ConfigMap extends Map[String, Any] with MapLike[String, Any, ConfigMap] with Serializable

A map of configuration data.

A ConfigMap can be populated from the Runner command line via -D arguments. Runner passes it to many methods where you can use it to configure your test runs. For example, Runner passed the ConfigMap to:

the apply method of Reporters via RunStarting events
the run method of Suite
the runNestedSuites method of Suite
the runTests method of Suite
the runTest method of Suite
the withFixture(NoArgTest) method of Suite
the withFixture(OneArgTest) method of fixture.Suite
the beforeEach(TestData) method of BeforeAndAfterEachTestData
the afterEach(TestData) method of BeforeAndAfterEachTestData

In addition to accessing the ConfigMap in overriden implementations of the above methods, you can also transform and pass along a modified ConfigMap.

A ConfigMap maps string keys to values of any type, i.e., it is a Map[String, Any]. To get a configuration value in a variable of the actual type of that value, therefore, you'll need to perform an unsafe cast. If this cast fails, you'll get an exception, which so long as the ConfigMap is used only in tests, will result in either a failed or canceled test or aborted suite. To give such exceptions nice stack depths and error messages, and to eliminate the need for using asInstanceOf in your test code, ConfigMap provides three methods for accessing values at expected types.

The getRequired method returns the value bound to a key cast to a specified type, or throws TestCanceledException if either the key is not bound or is bound to an incompatible type. Here's an example:

val tempFileName: String = configMap.getRequired[String]("tempFileName")

The getOptional method returns the value bound to a key cast to a specified type, wrapped in a Some, returns None if the key is not bound, or throws TestCanceledException if the key exists but is bound to an incompatible type. Here's an example:

val tempFileName: Option[String] = configMap.getOptional[String]("tempFileName")

The getWithDefault method returns the value bound to a key cast to a specified type, returns a specified default value if the key is not bound, or throws TestCanceledException if the key exists but is either not bound or is bound to an incompatible type. Here's an example:

val tempFileName: String = configMap.getWithDefault[String]("tempFileName", "tmp.txt")

final class ConfigMapWrapperSuite extends Suite

Wrapper Suite that passes an instance of the config map to the constructor of the wrapped Suite when run is invoked.

Recommended Usage: Trait ConfigMapWrapperSuite is primarily intended to be used with the "path" traits, which can't use the usual approaches to accessing the config map because of the eager manner in which they run tests.

Each time run is invoked on an instance of ConfigMapWrapperSuite, this suite will create a new instance of the suite to wrap, passing to the constructor the config map passed to run. This way, if the same ConfigMapWrapperSuite instance is run multiple times, each time with a different config map, an instance of the wrapped suite will be created for each config map. In addition to being passed to the wrapped suite's constructor, the config map passed to the ConfigMapWrapperSuite's run method will also be passed to the run method of the newly created wrapped suite instance.

The config map is accessible inside a Suite in many ways. It is passed to run, runNestedSuites, runTests, and runTest. It is also passed to withFixture, accessible via a method on NoArgTest and OneArgTest. It is passed to an overloaded forms of the beforeEach and afterEach methods of trait BeforeAndAfterEach, as well as overloaded forms of the beforeAll and afterAll methods of trait BeforeAndAfterAll. Tests themselves can have information taken from the config map, or the entire config map, through various means. The config map may be passed into the test via a ConfigMapFixture, for example. Class ConfigMapWrapperSuite represents one more way to get at the config map inside a suite of test: ConfigMapWrapperSuite will pass the config map to the constructor of your suite class, bringing it easily into scope for tests and helper methods alike.

Having the config map passed to the suite constructor might be more convenient in some cases, but in the case of the org.scalatest.path traits, it is necessary if a test needs information from a config map. The reason is that in a path trait, the test code is executed eagerly, before run is invoked. The results of the tests are registered when the tests are executed, and those results are merely reported once run is invoked. Thus by the time run has been invoked, it is too late to get the config map to the tests, which have already been executed. Using a ConfigMapWrapperSuite solves that problem. By passing the config map to the constructor, it is available early enough for the running tests to use it. Here's an example:

import org.scalatest._

@WrapWith(classOf[ConfigMapWrapperSuite])
class ExampleSpec(configMap: ConfigMap) extends path.FunSpec {

  describe("A widget database") {
    it("should contain consistent values") {
      val dbName = configMap("WidgetDbName") // Can access config map
      // ...
    }
  }
}

trait DiagrammedAssertions extends Assertions

Sub-trait of Assertions that override assert and assume methods to include a diagram showing the values of expression in the error message when the assertion or assumption fails.

Here are some examples:

scala> import DiagrammedAssertions._
import DiagrammedAssertions._

scala> assert(a == b || c >= d)
org.scalatest.exceptions.TestFailedException:

assert(a == b || c >= d)
       | |  | |  | |  |
       1 |  2 |  3 |  4
         |    |    false
         |    false
         false

        at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:422)
        ...

scala> assert(xs.exists(_ == 4))
org.scalatest.exceptions.TestFailedException:

assert(xs.exists(_ == 4))
       |  |
       |  false
       List(1, 2, 3)

        at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:422)
        ...

scala> assert("hello".startsWith("h") && "goodbye".endsWith("y"))
org.scalatest.exceptions.TestFailedException:

assert("hello".startsWith("h") && "goodbye".endsWith("y"))
       |       |          |    |  |         |        |
       "hello" true       "h"  |  "goodbye" false    "y"
                               false

        at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:422)
        ...

scala> assert(num.isInstanceOf[Int])
org.scalatest.exceptions.TestFailedException:

assert(num.isInstanceOf[Int])
       |   |
       1.0 false

        at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:422)
        ...

scala> assert(Some(2).isEmpty)
org.scalatest.exceptions.TestFailedException:

assert(Some(2).isEmpty)
       |    |  |
       |    2  false
       Some(2)

        at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:422)
        ...

scala> assert(None.isDefined)
org.scalatest.exceptions.TestFailedException:

assert(None.isDefined)
       |    |
       None false

        at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:422)
        ...

scala> assert(xs.exists(i => i > 10))
org.scalatest.exceptions.TestFailedException:

assert(xs.exists(i => i > 10))
       |  |
       |  false
       List(1, 2, 3)

        at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:422)
        ...

If the expression passed to assert or assume spans more than one line, DiagrammedAssertions falls back to the default style of error message, since drawing a diagram would be difficult. Here's an example showing how DiagrammedAssertions will treat a multi-line assertion (i.e., you don't get a diagram):

scala> assert("hello".startsWith("h") &&
     |   "goodbye".endsWith("y"))
org.scalatest.exceptions.TestFailedException: "hello" started with "h", but "goodbye" did not end with "y"
        at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:422)
        ...

Also, since an expression diagram essentially represents multi-line ascii art, if a clue string is provided, it appears above the diagram, not after it. It will often also show up in the diagram:

scala> assert(None.isDefined, "Don't do this at home")
org.scalatest.exceptions.TestFailedException: Don't do this at home

assert(None.isDefined, "Don't do this at home")
       |    |
       None false

        at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:422)
        ...

scala> assert(None.isDefined,
     |   "Don't do this at home")
org.scalatest.exceptions.TestFailedException: Don't do this at home

assert(None.isDefined,
       |    |
       None false

        at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:422)
        ...

Trait DiagrammedAssertions was inspired by Peter Niederwieser's work in Spock and Expecty.

trait DiagrammedExpr[T] extends AnyRef

A trait that represent an expression recorded by DiagrammedExprMacro, which includes the following members:

a boolean value
an anchor that records the position of this expression
anchor values of this expression (including sub-expressions)

DiagrammedExpr is used by code generated from DiagrammedAssertionsMacro, it needs to be public so that the generated code can be compiled. It is expected that ScalaTest users would ever need to use DiagrammedExpr directly.

trait DistributedSuiteSorter extends AnyRef

A sorter for the events of a run's distributed suites.

This trait is used, for example, when -PS is passed to Runner, to sort the events of distributed suites such that each suite's events are propagated together, with a timeout if an event takes too long.

trait DistributedTestSorter extends AnyRef

A sorter for the events of a suite's distributed tests.

This trait is used, for example, by ParallelTestExecution to sort the events of tests back into sequential order, with a timeout if an event takes too long.

trait Distributor extends AnyRef

Trait whose instances facilitate parallel execution of Suites.

Trait whose instances facilitate parallel execution of Suites. An optional Distributor is passed to the run method of Suite. If a Distributor is indeed passed, trait Suite's implementation of run will populate that Distributor with its nested Suites (by passing them to the Distributor's apply method) rather than executing the nested Suites directly. It is then up to another thread or process to execute those Suites.

If you have a set of nested Suites that must be executed sequentially, you can mix in trait SequentialNestedSuiteExecution, which overrides runNestedSuites and calls super's runNestedSuites implementation, passing in None for the Distributor.

Implementations of this trait must be thread safe.

trait DoNotDiscover extends Annotation

Annotation used to indicate that an otherwise discoverable test class should not be discovered.

Note: This is actually an annotation defined in Java, not a Scala trait. It must be defined in Java instead of Scala so it will be accessible at runtime. It has been inserted into Scaladoc by pretending it is a trait.

ScalaTest will discover any class that either extends Suite and has a public, no-arg constructor, or is annotated with a valid WrapWith annotation. If you wish to prevent a class from being discovered, simply annotate it with DoNotDiscover, like this:

import org.scalatest._

@DoNotDiscover
class SetSpec extends FlatSpec {

  "An empty Set" should "have size 0" in {
    assert(Set.empty.size === 0)
  }

  it should "produce NoSuchElementException when head is invoked" in {
    intercept[NoSuchElementException] {
      Set.empty.head
    }
  }
}

ScalaTest will run classes annotated with DoNotDiscover if asked to explicitly, it just won't discover them.

Note that because reflection is not supported on Scala.js, this annotation will only work on the JVM, not on Scala.js.

trait Documenter extends AnyRef

Trait to which markup text tests can be reported.

Note: Documenter will be described in more detail in a future 2.0 milestone release. As of this release you can't see its effects yet.

trait Documenting extends AnyRef

Trait that contains a markup method, which can be used to send markup to the Reporter.

final case class DynaTags(suiteTags: Map[String, Set[String]], testTags: Map[String, Map[String, Set[String]]]) extends Serializable with Product

Dynamic tags for a run.

Instances of this class are passed to the Filter constructor to support running selected suites and tests via dynamic tagging. For example, dynamic tags can be used to rerun tests that failed previously, or tests selected via a wildcard from Runner or the Scala interpreter.

suiteTags: a map from String suite ID to a set of tags for that suite.
testTags: a map from String suite ID to a map, whose keys are test names and values the tags for that test.

Exceptions thrown: NullPointerException if either suiteTags or testTags is null

trait EitherValues extends AnyRef

Trait that provides an implicit conversion that adds left.value and right.value methods to Either, which will return the selected value of the Either if defined, or throw TestFailedException if not.

This construct allows you to express in one statement that an Either should be left or right and that its value should meet some expectation. Here's are some examples:

either1.right.value should be > 9
either2.left.value should be ("Muchas problemas")

Or, using assertions instead of matcher expressions:

assert(either1.right.value > 9)
assert(either2.left.value === "Muchas problemas")

Were you to simply invoke right.get or left.get on the Either, if the Either wasn't defined as expected (e.g., it was a Left when you expected a Right), it would throw a NoSuchElementException:

val either: Either[String, Int] = Left("Muchas problemas")

either.right.get should be > 9 // either.right.get throws NoSuchElementException

The NoSuchElementException would cause the test to fail, but without providing a stack depth pointing to the failing line of test code. This stack depth, provided by TestFailedException (and a few other ScalaTest exceptions), makes it quicker for users to navigate to the cause of the failure. Without EitherValues, to get a stack depth exception you would need to make two statements, like this:

val either: Either[String, Int] = Left("Muchas problemas")

either should be ('right) // throws TestFailedException
either.right.get should be > 9

The EitherValues trait allows you to state that more concisely:

val either: Either[String, Int] = Left("Muchas problemas")

either.right.value should be > 9 // either.right.value throws TestFailedException

case class Entry[K, V](key: K, value: V) extends java.util.Map.Entry[K, V] with Product with Serializable

A case class implementation of java.util.Map.Entry to make it easier to test Java Maps with ScalaTest Matchers.

In Java, java.util.Map is not a subtype of java.util.Collection, and does not actually define an element type. You can ask a Java Map for an “entry set” via the entrySet method, which will return the Map's key/value pairs wrapped in a set of java.util.Map.Entry, but a Map is not actually a collection of Entry. To make Java Maps easier to work with, however, ScalaTest matchers allows you to treat a Java Map as a collection of Entry, and defines this convenience implementation of java.util.Map.Entry. Here's how you use it:

javaMap should contain (Entry(2, 3))
javaMap should contain oneOf (Entry(2, 3), Entry(3, 4))

key: the key of this entry
value: the value of this entry

sealed abstract class Exceptional extends Outcome

Superclass for the two outcomes of running a test that contain an exception: Failed and Canceled.

This class provides a toOption method that returns a Some wrapping the contained exception, and an isExceptional field with the value true. It's companion object provides an extractor that enables patterns that match a test that either failed or canceled, as in:

outcome match {
  case Exceptional(ex) => // handle failed or canceled case
  case _ => // handle succeeded, pending, or omitted case
}

case class Failed(exception: Throwable) extends Exceptional with Product with Serializable

Outcome for a test that failed, containing an exception describing the cause of the failure.

Note: the difference between this Failed class and the similarly named FailedStatus object is that an instance of this class indicates one test failed, whereas the FailedStatus object indicates either one or more tests failed and/or one or more suites aborted during a run. Both are used as the result type of Suite lifecycle methods, but Failed is a possible result of withFixture, whereas FailedStatus is a possible result of run, runNestedSuites, runTests, or runTest. In short, Failed is always just about one test, whereas FailedStatus could be about something larger: multiple tests or an entire suite.

class FeatureSpec extends FeatureSpecLike

A suite of tests in which each test represents one scenario of a feature.

A suite of tests in which each test represents one scenario of a feature. FeatureSpec is intended for writing tests that are "higher level" than unit tests, for example, integration tests, functional tests, and acceptance tests. You can use FeatureSpec for unit testing if you prefer, however.

Recommended Usage: Class FeatureSpec is primarily intended for acceptance testing, including facilitating the process of programmers working alongside non-programmers to define the acceptance requirements.

Although not required, FeatureSpec is often used together with GivenWhenThen to express acceptance requirements in more detail. Here's an example:

package org.scalatest.examples.featurespec

import org.scalatest._

class TVSet {
  private var on: Boolean = false
  def isOn: Boolean = on
  def pressPowerButton() {
    on = !on
  }
}

class TVSetSpec extends FeatureSpec with GivenWhenThen {

  info("As a TV set owner")
  info("I want to be able to turn the TV on and off")
  info("So I can watch TV when I want")
  info("And save energy when I'm not watching TV")

  feature("TV power button") {
    scenario("User presses power button when TV is off") {

      Given("a TV set that is switched off")
      val tv = new TVSet
      assert(!tv.isOn)

      When("the power button is pressed")
      tv.pressPowerButton()

      Then("the TV should switch on")
      assert(tv.isOn)
    }

    scenario("User presses power button when TV is on") {

      Given("a TV set that is switched on")
      val tv = new TVSet
      tv.pressPowerButton()
      assert(tv.isOn)

      When("the power button is pressed")
      tv.pressPowerButton()

      Then("the TV should switch off")
      assert(!tv.isOn)
    }
  }
}

Note: for more information on the calls to Given, When, and Then, see the documentation for trait GivenWhenThen and the Informers section below.

A FeatureSpec contains feature clauses and scenarios. You define a feature clause with feature, and a scenario with scenario. Both feature and scenario are methods, defined in FeatureSpec, which will be invoked by the primary constructor of TVSetSpec. A feature clause describes a feature of the subject (class or other entity) you are specifying and testing. In the previous example, the subject under specification and test is a TV set. The feature being specified and tested is the behavior of a TV set when its power button is pressed. With each scenario you provide a string (the spec text) that specifies the behavior of the subject for one scenario in which the feature may be used, and a block of code that tests that behavior. You place the spec text between the parentheses, followed by the test code between curly braces. The test code will be wrapped up as a function passed as a by-name parameter to scenario, which will register the test for later execution.

A FeatureSpec's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Scenarios can only be registered with the scenario method while the FeatureSpec is in its registration phase. Any attempt to register a scenario after the FeatureSpec has entered its ready phase, i.e., after run has been invoked on the FeatureSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using FeatureSpec is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Each scenario represents one test. The name of the test is the spec text passed to the scenario method. The feature name does not appear as part of the test name. In a FeatureSpec, therefore, you must take care to ensure that each test has a unique name (in other words, that each scenario has unique spec text).

When you run a FeatureSpec, it will send Formatters in the events it sends to the Reporter. ScalaTest's built-in reporters will report these events in such a way that the output is easy to read as an informal specification of the subject being tested. For example, were you to run TVSetSpec from within the Scala interpreter:

scala> org.scalatest.run(new TVSetSpec)

You would see:

TVSetSpec:
As a TV set owner
I want to be able to turn the TV on and off
So I can watch TV when I want
And save energy when I'm not watching TV
Feature: TV power button
  Scenario: User presses power button when TV is off
    Given a TV set that is switched off
    When the power button is pressed
    Then the TV should switch on
  Scenario: User presses power button when TV is on
    Given a TV set that is switched on
    When the power button is pressed
    Then the TV should switch off

Or, to run just the “Feature: TV power button Scenario: User presses power button when TV is on” method, you could pass that test's name, or any unique substring of the name, such as "TV is on". Here's an example:

scala> org.scalatest.run(new TVSetSpec, "TV is on")
TVSetSpec:
As a TV set owner
I want to be able to turn the TV on and off
So I can watch TV when I want
And save energy when I'm not watching TV
Feature: TV power button
  Scenario: User presses power button when TV is on
    Given a TV set that is switched on
    When the power button is pressed
    Then the TV should switch off

Note: Trait FeatureSpec's syntax is in part inspired by Cucumber, a Ruby BDD framework.

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, FeatureSpec provides registration methods that start with ignore instead of scenario. For example, to temporarily disable the test named addition, just change “scenario” into “ignore,” like this:

package org.scalatest.examples.featurespec.ignore

import org.scalatest.FeatureSpec

class TVSet {
  private var on: Boolean = false
  def isOn: Boolean = on
  def pressPowerButton() {
    on = !on
  }
}

class TVSetSpec extends FeatureSpec {

  feature("TV power button") {
    ignore("User presses power button when TV is off") {
      val tv = new TVSet
      assert(!tv.isOn)
      tv.pressPowerButton()
      assert(tv.isOn)
    }

    scenario("User presses power button when TV is on") {
      val tv = new TVSet
      tv.pressPowerButton()
      assert(tv.isOn)
      tv.pressPowerButton()
      assert(!tv.isOn)
    }
  }
}

If you run this version of SetSpec with:

scala> org.scalatest.run(new TVSetSpec)

It will run only the second scenario and report that the first scenario was ignored:

TVSetSpec:
Feature: TV power button
  Scenario: User presses power button when TV is off !!! IGNORED !!!
  Scenario: User presses power button when TV is on

Informers

One of the parameters to FeatureSpec's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the default reporting done by FeatureSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event.

One use case for the Informer is to pass more information about a scenario to the reporter. For example, the GivenWhenThen trait provides methods that use the implicit info provided by FeatureSpec to pass such information to the reporter. You can see this in action in the initial example of this trait's documentation.

Documenters

FeatureSpec also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example FlatSpec that uses markup:

package org.scalatest.examples.featurespec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends FeatureSpec with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

     def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  feature("An element can be added to an empty mutable Set") {
    scenario("When an element is added to an empty mutable Set") {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      markup("This test finished with a **bold** statement!")
    }
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.featurespec.note

import collection.mutable
import org.scalatest._

class SetSpec extends FeatureSpec {

  feature("An element can be added to an empty mutable Set") {
    scenario("When an element is added to an empty mutable Set") {

      info("info is recorded")
      markup("markup is *also* recorded")
      note("notes are sent immediately")
      alert("alerts are also sent immediately")

      val set = mutable.Set.empty[String]
      set += "clarity"
      assert(set.size === 1)
      assert(set.contains("clarity"))
    }
  }
}

Because note and alert information is sent immediately, it will appear before the test name in string reporters, and its color will be unrelated to the ultimate outcome of the test: note text will always appear in green, alert text will always appear in yellow. Here's an example:

scala> org.scalatest.run(new SetSpec)
SetSpec:
Feature: An element can be added to an empty mutable Set
  + notes are sent immediately
  + alerts are also sent immediately
  Scenario: When an element is added to an empty mutable Set
    info is recorded
  + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. The test can also include some code that sends more information about the behavior to the reporter when the tests run. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality, has not yet been implemented. You can mark tests as pending in a FeatureSpec like this:

package org.scalatest.examples.featurespec.pending

import org.scalatest.FeatureSpec

class TVSet {
  private var on: Boolean = false
  def isOn: Boolean = on
  def pressPowerButton() {
    on = !on
  }
}

class TVSetSpec extends FeatureSpec {

  feature("TV power button") {

    scenario("User presses power button when TV is off") (pending)

    scenario("User presses power button when TV is on") {
      val tv = new TVSet
      tv.pressPowerButton()
      assert(tv.isOn)
      tv.pressPowerButton()
      assert(!tv.isOn)
    }
  }
}

(Note: "(pending)" is the body of the test. Thus the test contains just one statement, an invocation of the pending method, which throws TestPendingException.) If you run this version of TVSetSpec with:

scala> org.scalatest.run(new TVSetSpec)

It will run both tests, but report that When empty should have size 0 is pending. You'll see:

TVSetSpec:
Feature: TV power button
  Scenario: User presses power button when TV is off (pending)
  Scenario: User presses power button when TV is on

One difference between an ignored test and a pending one is that an ignored test is intended to be used during a significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException. The reason for this difference is that it enables your unfinished test to send InfoProvided messages to the reporter before it completes abruptly with TestPendingException, as shown in the previous example on Informers that used the GivenWhenThen trait. For example, the following snippet in a FeatureSpec:

package org.scalatest.examples.featurespec.infopending

import org.scalatest._

class TVSet {
  private var on: Boolean = false

  def isOn: Boolean = on

  def pressPowerButton() {
    on = !on
  }
}

class TVSetSpec extends FeatureSpec with GivenWhenThen {

  info("As a TV set owner")
  info("I want to be able to turn the TV on and off")
  info("So I can watch TV when I want")
  info("And save energy when I'm not watching TV")

  feature("TV power button") {
    scenario("User presses power button when TV is off") {
      Given("a TV that is switched off")
      When("the power button is pressed")
      Then("the TV should switch on")
      pending
    }

    scenario("User presses power button when TV is on") {
      Given("a TV that is switched on")
      When("the power button is pressed")
      Then("the TV should switch off")
      pending
    }
  }
}

Would yield the following output when run in the interpreter:

scala> org.scalatest.run(new TVSetSpec)
TVSetSpec:
As a TV set owner
I want to be able to turn the TV on and off
So I can watch TV when I want
And save energy when I'm not watching TV
Feature: TV power button
  Scenario: User presses power button when TV is off (pending)
    Given a TV that is switched off
    When the power button is pressed
    Then the TV should switch on
  Scenario: User presses power button when TV is on (pending)
    Given a TV that is switched on
    When the power button is pressed
    Then the TV should switch off

Tagging tests

A FeatureSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing a FeatureSpec, groups of tests can optionally be included and/or excluded. To tag a FeatureSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for FeatureSpecs like this:

package org.scalatest.examples.featurespec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place FeatureSpec tests into groups with tags like this:

import org.scalatest.FeatureSpec
import org.scalatest.tagobjects.Slow

class TVSet {
  private var on: Boolean = false
  def isOn: Boolean = on
  def pressPowerButton() {
    on = !on
  }
}

class TVSetSpec extends FeatureSpec {

  feature("TV power button") {
    scenario("User presses power button when TV is off", Slow) {
      val tv = new TVSet
      assert(!tv.isOn)
      tv.pressPowerButton()
      assert(tv.isOn)
    }

    scenario("User presses power button when TV is on", Slow, DbTest) {
      val tv = new TVSet
      tv.pressPowerButton()
      assert(tv.isOn)
      tv.pressPowerButton()
      assert(!tv.isOn)
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of a FeatureSpec in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and more amenable for parallel test execution.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
fixture-context objects	By placing fixture methods and fields into traits, you can easily give each test just the newly created fixtures it needs by mixing together traits. Use this technique when you need different combinations of mutable fixture objects in different tests, and don't need to clean up after.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgTest)` instead)
`withFixture(OneArgTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or a holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.featurespec.getfixture

import org.scalatest.FeatureSpec
import collection.mutable.ListBuffer

class ExampleSpec extends FeatureSpec {

  class Fixture {
    val builder = new StringBuilder("ScalaTest is designed to ")
    val buffer = new ListBuffer[String]
  }

  def fixture = new Fixture

  feature("Simplicity") {
    scenario("User needs to read test code written by others") {
      val f = fixture
      f.builder.append("encourage clear code!")
      assert(f.builder.toString === "ScalaTest is designed to encourage clear code!")
      assert(f.buffer.isEmpty)
      f.buffer += "sweet"
    }

    scenario("User needs to understand what the tests are doing") {
      val f = fixture
      f.builder.append("be easy to reason about!")
      assert(f.builder.toString === "ScalaTest is designed to be easy to reason about!")
      assert(f.buffer.isEmpty)
    }
  }
}

The “f.” in front of each use of a fixture object provides a visual indication of which objects are part of the fixture, but if you prefer, you can import the the members with “import f._” and use the names directly.

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, you could pass in an initial value for a mutable fixture object as a parameter to the get-fixture method.

Instantiating fixture-context objects

An alternate technique that is especially useful when different tests need different combinations of fixture objects is to define the fixture objects as instance variables of fixture-context objects whose instantiation forms the body of tests. Like get-fixture methods, fixture-context objects are only appropriate if you don't need to clean up the fixtures after using them.

To use this technique, you define instance variables intialized with fixture objects in traits and/or classes, then in each test instantiate an object that contains just the fixture objects needed by the test. Traits allow you to mix together just the fixture objects needed by each test, whereas classes allow you to pass data in via a constructor to configure the fixture objects. Here's an example in which fixture objects are partitioned into two traits and each test just mixes together the traits it needs:

package org.scalatest.examples.featurespec.fixturecontext

import collection.mutable.ListBuffer
import org.scalatest.FeatureSpec

class ExampleSpec extends FeatureSpec {

  trait Builder {
    val builder = new StringBuilder("ScalaTest is designed to ")
  }

  trait Buffer {
    val buffer = ListBuffer("ScalaTest", "is", "designed", "to")
  }

  feature("Simplicity") {
    // This test needs the StringBuilder fixture
    scenario("User needs to read test code written by others") {
      new Builder {
        builder.append("encourage clear code!")
        assert(builder.toString === "ScalaTest is designed to encourage clear code!")
      }
    }

    // This test needs the ListBuffer[String] fixture
    scenario("User needs to understand what the tests are doing") {
      new Buffer {
        buffer += ("be", "easy", "to", "reason", "about!")
        assert(buffer === List("ScalaTest", "is", "designed", "to", "be", "easy", "to", "reason", "about!"))
      }
    }

    // This test needs both the StringBuilder and ListBuffer
    scenario("User needs to write tests") {
      new Builder with Buffer {
        builder.append("be easy to learn!")
        buffer += ("be", "easy", "to", "remember", "how", "to", "write!")
        assert(builder.toString === "ScalaTest is designed to be easy to learn!")
        assert(buffer === List("ScalaTest", "is", "designed", "to", "be", "easy",
          "to", "remember", "how", "to", "write!"))
      }
    }
  }
}

Overriding `withFixture(NoArgTest)`

Although the get-fixture method and fixture-context object approaches take care of setting up a fixture at the beginning of each test, they don't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgTest), one of ScalaTest's lifecycle methods defined in trait Suite.

Trait Suite's implementation of runTest passes a no-arg test function to withFixture(NoArgTest). It is withFixture's responsibility to invoke that test function. Suite's implementation of withFixture simply invokes the function, like this:

// Default implementation in trait Suite
protected def withFixture(test: NoArgTest) = {
  test()
}

You can, therefore, override withFixture to perform setup before and/or cleanup after invoking the test function. If you have cleanup to perform, you should invoke the test function inside a try block and perform the cleanup in a finally clause, in case an exception propagates back through withFixture. (If a test fails because of an exception, the test function invoked by withFixture will result in a Failed wrapping the exception. Nevertheless, best practice is to perform cleanup in a finally clause just in case an exception occurs.)

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. That is to say, instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgTest) = {
  // Perform setup
  try super.withFixture(test) // Invoke the test function
  finally {
    // Perform cleanup
  }
}

Here's an example in which withFixture(NoArgTest) is used to take a snapshot of the working directory if a test fails, and send that information to the reporter:

package org.scalatest.examples.featurespec.noargtest

import java.io.File
import org.scalatest._

class ExampleSpec extends FeatureSpec {

  override def withFixture(test: NoArgTest) = {

    super.withFixture(test) match {
      case failed: Failed =>
        val currDir = new File(".")
        val fileNames = currDir.list()
        info("Dir snapshot: " + fileNames.mkString(", "))
        failed
      case other => other
    }
  }

  scenario("This scenario should succeed") {
    assert(1 + 1 === 2)
  }

  scenario("This scenario should fail") {
    assert(1 + 1 === 3)
  }
}

Running this version of ExampleSuite in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSpec)
ExampleSpec:
Scenario: This scenario should succeed
Scenario: This scenario should fail *** FAILED ***
  2 did not equal 3 (:115)
  + Dir snapshot: hello.txt, world.txt

Note that the NoArgTest passed to withFixture, in addition to an apply method that executes the test, also includes the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

package org.scalatest.examples.featurespec.loanfixture

import java.util.concurrent.ConcurrentHashMap

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer
    databases.put(name, db)
    db
  }
  def removeDb(name: String) {
    databases.remove(name)
  }
}

import org.scalatest.FeatureSpec
import DbServer._
import java.util.UUID.randomUUID
import java.io._

class ExampleSpec extends FeatureSpec {

  def withDatabase(testCode: Db => Any) {
    val dbName = randomUUID.toString
    val db = createDb(dbName) // create the fixture
    try {
      db.append("ScalaTest is designed to ") // perform setup
      testCode(db) // "loan" the fixture to the test
    }
    finally removeDb(dbName) // clean up the fixture
  }

  def withFile(testCode: (File, FileWriter) => Any) {
    val file = File.createTempFile("hello", "world") // create the fixture
    val writer = new FileWriter(file)
    try {
      writer.write("ScalaTest is designed to ") // set up the fixture
      testCode(file, writer) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  feature("Simplicity") {
    // This test needs the file fixture
    scenario("User needs to read test code written by others") {
      withFile { (file, writer) =>
        writer.write("encourage clear code!")
        writer.flush()
        assert(file.length === 46)
      }
    }
    // This test needs the database fixture
    scenario("User needs to understand what the tests are doing") {
      withDatabase { db =>
        db.append("be easy to reason about!")
        assert(db.toString === "ScalaTest is designed to be easy to reason about!")
      }
    }
    // This test needs both the file and the database
    scenario("User needs to write tests") {
      withDatabase { db =>
        withFile { (file, writer) => // loan-fixture methods compose
          db.append("be easy to learn!")
          writer.write("be easy to remember how to write!")
          writer.flush()
          assert(db.toString === "ScalaTest is designed to be easy to learn!")
          assert(file.length === 58)
        }
      }
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating files or databases, it is a good idea to give each file or database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.FeatureSpec and overriding withFixture(OneArgTest). Each test in a fixture.FeatureSpec takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgTest. This withFixture method is responsible for invoking the one-arg test function, so you can perform fixture set up before, and clean up after, invoking and passing the fixture into the test function.

To enable the stacking of traits that define withFixture(NoArgTest), it is a good idea to let withFixture(NoArgTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgTest to a NoArgTest. You can do that by passing the fixture object to the toNoArgTest method of OneArgTest. In other words, instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgTest) method of the same instance by writing:

withFixture(test.toNoArgTest(theFixture))

Here's a complete example:

package org.scalatest.examples.featurespec.oneargtest

import org.scalatest.fixture
import java.io._

class ExampleSpec extends fixture.FeatureSpec {

  case class FixtureParam(file: File, writer: FileWriter)

  def withFixture(test: OneArgTest) = {

    // create the fixture
    val file = File.createTempFile("hello", "world")
    val writer = new FileWriter(file)
    val theFixture = FixtureParam(file, writer)

    try {
      writer.write("ScalaTest is designed to be ") // set up the fixture
      withFixture(test.toNoArgTest(theFixture)) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  feature("Simplicity") {
    scenario("User needs to read test code written by others") { f =>
      f.writer.write("encourage clear code!")
      f.writer.flush()
      assert(f.file.length === 49)
    }

    scenario("User needs to understand what the tests are doing") { f =>
      f.writer.write("be easy to reason about!")
      f.writer.flush()
      assert(f.file.length === 52)
    }
  }
}

In this example, the tests actually required two fixture objects, a File and a FileWriter. In such situations you can simply define the FixtureParam type to be a tuple containing the objects, or as is done in this example, a case class containing the objects. For more information on the withFixture(OneArgTest) technique, see the documentation for fixture.FeatureSpec.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.featurespec.beforeandafter

import org.scalatest._
import collection.mutable.ListBuffer

class ExampleSpec extends FeatureSpec with BeforeAndAfter {

  val builder = new StringBuilder
  val buffer = new ListBuffer[String]

  before {
    builder.append("ScalaTest is designed to ")
  }

  after {
    builder.clear()
    buffer.clear()
  }

  feature("Simplicity") {
    scenario("User needs to read test code written by others") {
      builder.append("encourage clear code!")
      assert(builder.toString === "ScalaTest is designed to encourage clear code!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    scenario("User needs to understand what the tests are doing") {
      builder.append("be easy to reason about!")
      assert(builder.toString === "ScalaTest is designed to be easy to reason about!")
      assert(buffer.isEmpty)
    }
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state. This is why ScalaTest's ParallelTestExecution trait extends OneInstancePerTest. By running each test in its own instance of the class, each test has its own copy of the instance variables, so you don't need to synchronize. If you mixed ParallelTestExecution into the ExampleSuite above, the tests would run in parallel just fine without any synchronization needed on the mutable StringBuilder and ListBuffer[String] objects.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilder and ListBuffer[String] fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.featurespec.composingwithfixture

import org.scalatest._
import collection.mutable.ListBuffer

trait Builder extends TestSuiteMixin { this: TestSuite =>

  val builder = new StringBuilder

  abstract override def withFixture(test: NoArgTest) = {
    builder.append("ScalaTest is designed to ")
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally builder.clear()
  }
}

trait Buffer extends TestSuiteMixin { this: TestSuite =>

  val buffer = new ListBuffer[String]

  abstract override def withFixture(test: NoArgTest) = {
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally buffer.clear()
  }
}

class ExampleSpec extends FeatureSpec with Builder with Buffer {

  feature("Simplicity") {
    scenario("User needs to read test code written by others") {
      builder.append("encourage clear code!")
      assert(builder.toString === "ScalaTest is designed to encourage clear code!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }

    scenario("User needs to understand what the tests are doing") {
      builder.append("be easy to reason about!")
      assert(builder.toString === "ScalaTest is designed to be easy to reason about!")
      assert(buffer.isEmpty)
      buffer += "easy"
    }
  }
}

By mixing in both the Builder and Buffer traits, ExampleSuite gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Spec extends FeatureSpec with Buffer with Builder

And if you only need one fixture you mix in only that trait:

class Example3Spec extends FeatureSpec with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.featurespec.composingbeforeandaftereach

import org.scalatest._
import collection.mutable.ListBuffer

trait Builder extends BeforeAndAfterEach { this: Suite =>

  val builder = new StringBuilder

  override def beforeEach() {
    builder.append("ScalaTest is designed to ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builder.clear()
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  val buffer = new ListBuffer[String]

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally buffer.clear()
  }
}

class ExampleSpec extends FeatureSpec with Builder with Buffer {

  feature("Simplicity") {
    scenario("User needs to read test code written by others") {
      builder.append("encourage clear code!")
      assert(builder.toString === "ScalaTest is designed to encourage clear code!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }

    scenario("User needs to understand what the tests are doing") {
      builder.append("be easy to reason about!")
      assert(builder.toString === "ScalaTest is designed to be easy to reason about!")
      assert(buffer.isEmpty)
      buffer += "easy"
    }
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared scenarios

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in a FeatureSpec, you first place shared tests (i.e., shared scenarios) in behavior functions. These behavior functions will be invoked during the construction phase of any FeatureSpec that uses them, so that the scenarios they contain will be registered as scenarios in that FeatureSpec. For example, given this stack class:

import scala.collection.mutable.ListBuffer

class Stack[T] {

  val MAX = 10
  private val buf = new ListBuffer[T]

  def push(o: T) {
    if (!full)
      buf.prepend(o)
    else
      throw new IllegalStateException("can't push onto a full stack")
  }

  def pop(): T = {
    if (!empty)
      buf.remove(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def peek: T = {
    if (!empty)
      buf(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def full: Boolean = buf.size == MAX
  def empty: Boolean = buf.size == 0
  def size = buf.size

  override def toString = buf.mkString("Stack(", ", ", ")")
}

You may want to test the Stack class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several scenarios that make sense any time the stack is non-empty. Thus you'd ideally want to run those same scenarios for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these scenarios out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your FeatureSpec for stack, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared scenarios are run for all three fixtures.

You can define a behavior function that encapsulates these shared scenarios inside the FeatureSpec that uses them. If they are shared between different FeatureSpecs, however, you could also define them in a separate trait that is mixed into each FeatureSpec that uses them. For example, here the nonEmptyStack behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared scenarios for non-full stacks:

import org.scalatest.FeatureSpec
import org.scalatest.GivenWhenThen
import org.scalatestexamples.helpers.Stack

trait FeatureSpecStackBehaviors { this: FeatureSpec with GivenWhenThen =>

  def nonEmptyStack(createNonEmptyStack: => Stack[Int], lastItemAdded: Int) {

    scenario("empty is invoked on this non-empty stack: " + createNonEmptyStack.toString) {

      Given("a non-empty stack")
      val stack = createNonEmptyStack

      When("empty is invoked on the stack")
      Then("empty returns false")
      assert(!stack.empty)
    }

    scenario("peek is invoked on this non-empty stack: " + createNonEmptyStack.toString) {

      Given("a non-empty stack")
      val stack = createNonEmptyStack
      val size = stack.size

      When("peek is invoked on the stack")
      Then("peek returns the last item added")
      assert(stack.peek === lastItemAdded)

      And("the size of the stack is the same as before")
      assert(stack.size === size)
    }

    scenario("pop is invoked on this non-empty stack: " + createNonEmptyStack.toString) {

      Given("a non-empty stack")
      val stack = createNonEmptyStack
      val size = stack.size

      When("pop is invoked on the stack")
      Then("pop returns the last item added")
      assert(stack.pop === lastItemAdded)

      And("the size of the stack one less than before")
      assert(stack.size === size - 1)
    }
  }

  def nonFullStack(createNonFullStack: => Stack[Int]) {

    scenario("full is invoked on this non-full stack: " + createNonFullStack.toString) {

      Given("a non-full stack")
      val stack = createNonFullStack

      When("full is invoked on the stack")
      Then("full returns false")
      assert(!stack.full)
    }

    scenario("push is invoked on this non-full stack: " + createNonFullStack.toString) {

      Given("a non-full stack")
      val stack = createNonFullStack
      val size = stack.size

      When("push is invoked on the stack")
      stack.push(7)

      Then("the size of the stack is one greater than before")
      assert(stack.size === size + 1)

      And("the top of the stack contains the pushed value")
      assert(stack.peek === 7)
    }
  }
}

Given these behavior functions, you could invoke them directly, but FeatureSpec offers a DSL for the purpose, which looks like this:

scenariosFor(nonEmptyStack(stackWithOneItem, lastValuePushed))
scenariosFor(nonFullStack(stackWithOneItem))

If you prefer to use an imperative style to change fixtures, for example by mixing in BeforeAndAfterEach and reassigning a stack var in beforeEach, you could write your behavior functions in the context of that var, which means you wouldn't need to pass in the stack fixture because it would be in scope already inside the behavior function. In that case, your code would look like this:

scenariosFor(nonEmptyStack) // assuming lastValuePushed is also in scope inside nonEmptyStack
scenariosFor(nonFullStack)

The recommended style, however, is the functional, pass-all-the-needed-values-in style. Here's an example:

import org.scalatest.FeatureSpec
import org.scalatest.GivenWhenThen
import org.scalatestexamples.helpers.Stack

class StackFeatureSpec extends FeatureSpec with GivenWhenThen with FeatureSpecStackBehaviors {

  // Stack fixture creation methods
  def emptyStack = new Stack[Int]

  def fullStack = {
    val stack = new Stack[Int]
    for (i <- 0 until stack.MAX)
      stack.push(i)
    stack
  }

  def stackWithOneItem = {
    val stack = new Stack[Int]
    stack.push(9)
    stack
  }

  def stackWithOneItemLessThanCapacity = {
    val stack = new Stack[Int]
    for (i <- 1 to 9)
      stack.push(i)
    stack
  }

  val lastValuePushed = 9

  feature("A Stack is pushed and popped") {

    scenario("empty is invoked on an empty stack") {

      Given("an empty stack")
      val stack = emptyStack

      When("empty is invoked on the stack")
      Then("empty returns true")
      assert(stack.empty)
    }

    scenario("peek is invoked on an empty stack") {

      Given("an empty stack")
      val stack = emptyStack

      When("peek is invoked on the stack")
      Then("peek throws IllegalStateException")
      assertThrows[IllegalStateException] {
        stack.peek
      }
    }

    scenario("pop is invoked on an empty stack") {

      Given("an empty stack")
      val stack = emptyStack

      When("pop is invoked on the stack")
      Then("pop throws IllegalStateException")
      assertThrows[IllegalStateException] {
        emptyStack.pop
      }
    }

    scenariosFor(nonEmptyStack(stackWithOneItem, lastValuePushed))
    scenariosFor(nonFullStack(stackWithOneItem))

    scenariosFor(nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed))
    scenariosFor(nonFullStack(stackWithOneItemLessThanCapacity))

    scenario("full is invoked on a full stack") {

      Given("an full stack")
      val stack = fullStack

      When("full is invoked on the stack")
      Then("full returns true")
      assert(stack.full)
    }

    scenariosFor(nonEmptyStack(fullStack, lastValuePushed))

    scenario("push is invoked on a full stack") {

      Given("an full stack")
      val stack = fullStack

      When("push is invoked on the stack")
      Then("push throws IllegalStateException")
      assertThrows[IllegalStateException] {
        stack.push(10)
      }
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> (new StackFeatureSpec).execute()
Feature: A Stack is pushed and popped
  Scenario: empty is invoked on an empty stack
    Given an empty stack
    When empty is invoked on the stack
    Then empty returns true
  Scenario: peek is invoked on an empty stack
    Given an empty stack
    When peek is invoked on the stack
    Then peek throws IllegalStateException
  Scenario: pop is invoked on an empty stack
    Given an empty stack
    When pop is invoked on the stack
    Then pop throws IllegalStateException
  Scenario: empty is invoked on this non-empty stack: Stack(9)
    Given a non-empty stack
    When empty is invoked on the stack
    Then empty returns false
  Scenario: peek is invoked on this non-empty stack: Stack(9)
    Given a non-empty stack
    When peek is invoked on the stack
    Then peek returns the last item added
    And the size of the stack is the same as before
  Scenario: pop is invoked on this non-empty stack: Stack(9)
    Given a non-empty stack
    When pop is invoked on the stack
    Then pop returns the last item added
    And the size of the stack one less than before
  Scenario: full is invoked on this non-full stack: Stack(9)
    Given a non-full stack
    When full is invoked on the stack
    Then full returns false
  Scenario: push is invoked on this non-full stack: Stack(9)
    Given a non-full stack
    When push is invoked on the stack
    Then the size of the stack is one greater than before
    And the top of the stack contains the pushed value
  Scenario: empty is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
    Given a non-empty stack
    When empty is invoked on the stack
    Then empty returns false
  Scenario: peek is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
    Given a non-empty stack
    When peek is invoked on the stack
    Then peek returns the last item added
    And the size of the stack is the same as before
  Scenario: pop is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
    Given a non-empty stack
    When pop is invoked on the stack
    Then pop returns the last item added
    And the size of the stack one less than before
  Scenario: full is invoked on this non-full stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
    Given a non-full stack
    When full is invoked on the stack
    Then full returns false
  Scenario: push is invoked on this non-full stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
    Given a non-full stack
    When push is invoked on the stack
    Then the size of the stack is one greater than before
    And the top of the stack contains the pushed value
  Scenario: full is invoked on a full stack
    Given an full stack
    When full is invoked on the stack
    Then full returns true
  Scenario: empty is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
    Given a non-empty stack
    When empty is invoked on the stack
    Then empty returns false
  Scenario: peek is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
    Given a non-empty stack
    When peek is invoked on the stack
    Then peek returns the last item added
    And the size of the stack is the same as before
  Scenario: pop is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
    Given a non-empty stack
    When pop is invoked on the stack
    Then pop returns the last item added
    And the size of the stack one less than before
  Scenario: push is invoked on a full stack
    Given an full stack
    When push is invoked on the stack
    Then push throws IllegalStateException

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. Although in a FeatureSpec, the feature clause is a nesting construct analogous to FunSpec's describe clause, you many sometimes need to do a bit of extra work to ensure that the test names are unique. If a duplicate test name problem shows up in a FeatureSpec, you can pass in a prefix or suffix string to add to each test name. You can pass this string the same way you pass any other data needed by the shared tests, or just call toString on the shared fixture object. This is the approach taken by the previous FeatureSpecStackBehaviors example.

Given this FeatureSpecStackBehaviors trait, calling it with the stackWithOneItem fixture, like this:

scenariosFor(nonEmptyStack(stackWithOneItem, lastValuePushed))

yields test names:

empty is invoked on this non-empty stack: Stack(9)
peek is invoked on this non-empty stack: Stack(9)
pop is invoked on this non-empty stack: Stack(9)

Whereas calling it with the stackWithOneItemLessThanCapacity fixture, like this:

scenariosFor(nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed))

yields different test names:

empty is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
peek is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
pop is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)

trait FeatureSpecLike extends TestSuite with TestRegistration with Informing with Notifying with Alerting with Documenting

Implementation trait for class FeatureSpec, which represents a suite of tests in which each test represents one scenario of a feature.

FeatureSpec is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of FeatureSpec into some other class, you can use this trait instead, because class FeatureSpec does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of FeatureSpec.

final class Filter extends Serializable

Filter whose apply method determines which of the passed tests to run and ignore based on tags to include and exclude passed as as class parameters.

This class handles the org.scalatest.Ignore tag specially, in that its apply method indicates which tests should be ignored based on whether they are tagged with org.scalatest.Ignore. If "org.scalatest.Ignore" is not passed in the tagsToExclude set, it will be implicitly added. However, if the tagsToInclude option is defined, and the contained set does not include "org.scalatest.Ignore", then only those tests that are both tagged with org.scalatest.Ignore and at least one of the tags in the tagsToInclude set will be included in the result of apply and marked as ignored (so long as the test is not also marked with a tag other than org.scalatest.Ignore that is a member of the tagsToExclude set. For example, if SlowAsMolasses is a member of the tagsToInclude set and a test is tagged with both org.scalatest.Ignore and SlowAsMolasses, and SlowAsMolasses appears in the tagsToExclude set, the SlowAsMolasses tag will "overpower" the org.scalatest.Ignore tag, and the test will be filtered out entirely rather than being ignored.

Exceptions thrown: IllegalArgumentException if tagsToInclude is defined, but contains an empty set
NullArgumentException if either tagsToInclude or tagsToExclude are null

trait Finders extends Annotation

Annotation used to mark a trait or class as defining a testing style that has a org.scalatest.finders.Finder implementation, which IDEs and other tools can use to discover tests and scopes.

Note: This is actually an annotation defined in Java, not a Scala trait. It must be defined in Java instead of Scala so it will be accessible at runtime. It has been inserted into Scaladoc by pretending it is a trait.

This annotation is used to enable different styles of testing, including both native ScalaTest styles and custom user-created styles, to have rich IDE support. The "Finder API" is released separately from ScalaTest proper, because it is only used by tools such as IDEs.

trait FixtureContext extends scalatest.compatible.Assertion

Marker trait for fixture-context objects, that enables them to be used in testing styles that require type Assertion

A fixture-context object is a way to share fixtures between different tests that is most useful when different tests need different combinations of fixture objects. The fixture-context object technique is only appropriate if you don't need to clean up the fixtures after using them.

To use this technique, you define instance variables intialized with fixture objects in traits and/or classes, then in each test instantiate an object that contains just the fixture objects needed by the test. Traits allow you to mix together just the fixture objects needed by each test, whereas classes allow you to pass data in via a constructor to configure the fixture objects. Here's an example FlatSpec in which fixture objects are partitioned into two traits and each test just mixes together the traits it needs:

package org.scalatest.examples.flatspec.fixturecontext

import collection.mutable.ListBuffer
import org.scalatest.FlatSpec
import org.scalatest.FixtureContext

class ExampleSpec extends FlatSpec {

  trait Builder extends FixtureContext {
    val builder = new StringBuilder("ScalaTest is ")
  }

  trait Buffer extends FixtureContext {
    val buffer = ListBuffer("ScalaTest", "is")
  }

  // This test needs the StringBuilder fixture
  "Testing" should "be productive" in new Builder {
    builder.append("productive!")
    assert(builder.toString === "ScalaTest is productive!")
  }

  // This test needs the ListBuffer[String] fixture
  "Test code" should "be readable" in new Buffer {
    buffer += ("readable!")
    assert(buffer === List("ScalaTest", "is", "readable!"))
  }

  // This test needs both the StringBuilder and ListBuffer
  it should "be clear and concise" in new Builder with Buffer {
    builder.append("clear!")
    buffer += ("concise!")
    assert(builder.toString === "ScalaTest is clear!")
    assert(buffer === List("ScalaTest", "is", "concise!"))
  }
}

Extending FixtureContext, which extends trait org.scalatest.compatible.Assertion makes it more convenient to use fixture-context objects in styles, such as async styles, that require test bodies to have type Assertion.

class FlatSpec extends FlatSpecLike

Facilitates a “behavior-driven” style of development (BDD), in which tests are combined with text that specifies the behavior the tests verify.

Recommended Usage: Class FlatSpec is a good first step for teams wishing to move from xUnit to BDD, because its structure is flat like xUnit, so simple and familiar, but the test names must be written in a specification style: “X should Y,” “A must B,” etc.

Trait FlatSpec is so named because your specification text and tests line up flat against the left-side indentation level, with no nesting needed. Here's an example FlatSpec:

package org.scalatest.examples.flatspec

import org.scalatest.FlatSpec

class SetSpec extends FlatSpec {

  behavior of "An empty Set"

  it should "have size 0" in {
    assert(Set.empty.size === 0)
  }

  it should "produce NoSuchElementException when head is invoked" in {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

Note: you can use must or can as well as should in a FlatSpec. For example, instead of it should "have..., you could write it must "have... or it can "have....

Instead of using a behavior of clause, you can alternatively use a shorthand syntax in which you replace the first it with the subject string, like this:

package org.scalatest.examples.flatspec

import org.scalatest.FlatSpec

class SetSpec extends FlatSpec {

  "An empty Set" should "have size 0" in {
    assert(Set.empty.size === 0)
  }

  it should "produce NoSuchElementException when head is invoked" in {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

Running either of the two previous versions of SetSpec in the Scala interpreter would yield:

An empty Set
- should have size 0
- should produce NoSuchElementException when head is invoked

In a FlatSpec you write a one (or more) sentence specification for each bit of behavior you wish to specify and test. Each specification sentence has a "subject," which is sometimes called the system under test (or SUT). The subject is the entity being specified and tested and also serves as the subject of the sentences you write for each test. Often you will want to write multiple tests for the same subject. In a FlatSpec, you name the subject once, with a behavior of clause or its shorthand, then write tests for that subject with it should/must/can "do something" phrases. Each it refers to the most recently declared subject. For example, the four tests shown in this snippet are all testing a stack that contains one item:

behavior of "A Stack (with one item)"

it should "be non-empty" in {}

it should "return the top item on peek" in {}

it should "not remove the top item on peek" in {}

it should "remove the top item on pop" in {}

The same is true if the tests are written using the shorthand notation:

"A Stack (with one item)" should "be non-empty" in {}

it should "return the top item on peek" in {}

it should "not remove the top item on peek" in {}

it should "remove the top item on pop" in {}

In a FlatSpec, therefore, to figure out what "it" means, you just scan vertically until you find the most recent use of behavior of or the shorthand notation.

Because sometimes the subject could be plural, you can alternatively use they instead of it:

"The combinators" should "be easy to learn" in {}

they should "be efficient" in {}

they should "do something cool" in {}

A FlatSpec's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Tests can only be registered while the FlatSpec is in its registration phase. Any attempt to register a test after the FlatSpec has entered its ready phase, i.e., after run has been invoked on the FlatSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using FlatSpec is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, FlatSpec provides a method ignore that can be used instead of it or they to register a test. For example, to temporarily disable the test with the name "An empty Set should produce NoSuchElementException when head is invoked", just change “it” into “ignore,” like this:

package org.scalatest.examples.flatspec.ignore

import org.scalatest.FlatSpec

class SetSpec extends FlatSpec {

  "An empty Set" should "have size 0" in {
    assert(Set.empty.size === 0)
  }

  ignore should "produce NoSuchElementException when head is invoked" in {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

If you run this version of SetSpec with:

scala> org.scalatest.run(new SetSpec)

It will run only the first test and report that the second test was ignored:

An empty Set
- should have size 0
- should produce NoSuchElementException when head is invoked !!! IGNORED !!!

When using shorthand notation, you won't have an it to change into ignore for the first test of each new subject. To ignore such tests, you must instead change in to ignore. For example, to temporarily disable the test with the name "An empty Set should have size 0", change “in” into “ignore” like this:

package org.scalatest.examples.flatspec.ignoreafter

import org.scalatest.FlatSpec

class SetSpec extends FlatSpec {

  "An empty Set" should "have size 0" ignore {
    assert(Set.empty.size === 0)
  }

  it should "produce NoSuchElementException when head is invoked" in {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

If you run this version of StackSpec with:

scala> org.scalatest.run(new SetSpec)

It will run only the second test and report that the first test was ignored:

An empty Set
- should have size 0 !!! IGNORED !!!
- should produce NoSuchElementException when head is invoked

If you wish to temporarily ignore an entire suite of tests, you can (on the JVM, not Scala.js) annotate the test class with @Ignore, like this:

package org.scalatest.examples.flatspec.ignoreall

import org.scalatest._

@Ignore
class SetSpec extends FlatSpec {

  "An empty Set" should "have size 0" in {
    assert(Set.empty.size === 0)
  }

  it should "produce NoSuchElementException when head is invoked" in {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the SetSpec in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above SetSpec in the Scala interpreter, you'll see:

scala> org.scalatest.run(new SetSpec)
SetSpec:
An empty Set
- should have size 0 !!! IGNORED !!!
- should produce NoSuchElementException when head is invoked !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class visible, to encourage the developers to eventually fix and “un-ignore” it. If you want to prevent a class from being discovered at all (on the JVM, not Scala.js), use the DoNotDiscover annotation instead.

Informers

One of the parameters to FlatSpec's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the reporting done by default by FlatSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event.

One use case for the Informer is to pass more information about a specification to the reporter. For example, the GivenWhenThen trait provides methods that use the implicit info provided by FlatSpec to pass such information to the reporter. Here's an example:

package org.scalatest.examples.flatspec.info

import collection.mutable
import org.scalatest._

class SetSpec extends FlatSpec with GivenWhenThen {

  "A mutable Set" should "allow an element to be added" in {
    Given("an empty mutable Set")
    val set = mutable.Set.empty[String]

    When("an element is added")
    set += "clarity"

    Then("the Set should have size 1")
    assert(set.size === 1)

    And("the Set should contain the added element")
    assert(set.contains("clarity"))

    info("That's all folks!")
  }
}

If you run this FlatSpec from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSpec)
SetSpec:
A mutable Set
- should allow an element to be added
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

Documenters

FlatSpec also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example FlatSpec that uses markup:

package org.scalatest.examples.flatspec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends FlatSpec with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

    def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  "A mutable Set" should "allow an element to be added" in {
    Given("an empty mutable Set")
    val set = mutable.Set.empty[String]

    When("an element is added")
    set += "clarity"

    Then("the Set should have size 1")
    assert(set.size === 1)

    And("the Set should contain the added element")
    assert(set.contains("clarity"))

    markup("This test finished with a **bold** statement!")
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.flatspec.note

import collection.mutable
import org.scalatest._

class SetSpec extends FlatSpec {

  "A mutable Set" should "allow an element to be added" in {

    info("info is recorded")
    markup("markup is *also* recorded")
    note("notes are sent immediately")
    alert("alerts are also sent immediately")

    val set = mutable.Set.empty[String]
    set += "clarity"
    assert(set.size === 1)
    assert(set.contains("clarity"))
  }
}

Because note and alert information is sent immediately, it will appear before the test name in string reporters, and its color will be unrelated to the ultimate outcome of the test: note text will always appear in green, alert text will always appear in yellow. Here's an example:

scala> org.scalatest.run(new SetSpec)
SetSpec:
A mutable Set
  + notes are sent immediately
  + alerts are also sent immediately
- should allow an element to be added
  + info is recorded
  + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. The test can also include some code that sends more information about the behavior to the reporter when the tests run. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality it is intended to test, has not yet been implemented. You can mark tests as pending in FlatSpec like this:

package org.scalatest.examples.flatspec.pending

import org.scalatest._

class SetSpec extends FlatSpec {

  "An empty Set" should "have size 0" in (pending)

  it should "produce NoSuchElementException when head is invoked" in {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

If you run this version of FlatSpec with:

scala> org.scalatest.run(new SetSpec)

It will run both tests but report that An empty Set should have size 0 is pending. You'll see:

An empty Set
- should have size 0 (pending)
- should produce NoSuchElementException when head is invoked

One difference between an ignored test and a pending one is that an ignored test is intended to be used during a significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException. The reason for this difference is that it enables your unfinished test to send InfoProvided messages to the reporter before it completes abruptly with TestPendingException, as shown in the previous example on Informers that used the GivenWhenThen trait. For example, the following snippet in a FlatSpec:

"The Scala language" must "add correctly" in {
   Given("two integers")
   When("they are added")
   Then("the result is the sum of the two numbers")
   pending
 }
 // ...

Would yield the following output when run in the interpreter:

The Scala language
- must add correctly (pending)
  + Given two integers
  + When they are added
  + Then the result is the sum of the two numbers

Tagging tests

A FlatSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing a FlatSpec, groups of tests can optionally be included and/or excluded. To tag a FlatSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for FlatSpecs like this:

package org.scalatest.examples.flatspec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place FlatSpec tests into groups with tags like this:

import org.scalatest.FlatSpec
import org.scalatest.tagobjects.Slow

class SetSpec extends FlatSpec {

  behavior of "An empty Set"

  it should "have size 0" taggedAs(Slow) in {
    assert(Set.empty.size === 0)
  }

  it should "produce NoSuchElementException when head is invoked" taggedAs(Slow, DbTest) in {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of a FlatSpec in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and more amenable for parallel test execution.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
fixture-context objects	By placing fixture methods and fields into traits, you can easily give each test just the newly created fixtures it needs by mixing together traits. Use this technique when you need different combinations of mutable fixture objects in different tests, and don't need to clean up after.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgTest)` instead)
`withFixture(OneArgTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or a holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.flatspec.getfixture

import org.scalatest.FlatSpec
import collection.mutable.ListBuffer

class ExampleSpec extends FlatSpec {

  class Fixture {
    val builder = new StringBuilder("ScalaTest is ")
    val buffer = new ListBuffer[String]
  }

  def fixture = new Fixture

  "Testing" should "be easy" in {
    val f = fixture
    f.builder.append("easy!")
    assert(f.builder.toString === "ScalaTest is easy!")
    assert(f.buffer.isEmpty)
    f.buffer += "sweet"
  }

  it should "be fun" in {
    val f = fixture
    f.builder.append("fun!")
    assert(f.builder.toString === "ScalaTest is fun!")
    assert(f.buffer.isEmpty)
  }
}

The “f.” in front of each use of a fixture object provides a visual indication of which objects are part of the fixture, but if you prefer, you can import the the members with “import f._” and use the names directly.

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, if you could pass in an initial value for a mutable fixture object as a parameter to the get-fixture method.

Instantiating fixture-context objects

An alternate technique that is especially useful when different tests need different combinations of fixture objects is to define the fixture objects as instance variables of fixture-context objects whose instantiation forms the body of tests. Like get-fixture methods, fixture-context objects are only appropriate if you don't need to clean up the fixtures after using them.

To use this technique, you define instance variables intialized with fixture objects in traits and/or classes, then in each test instantiate an object that contains just the fixture objects needed by the test. Traits allow you to mix together just the fixture objects needed by each test, whereas classes allow you to pass data in via a constructor to configure the fixture objects. Here's an example in which fixture objects are partitioned into two traits and each test just mixes together the traits it needs:

package org.scalatest.examples.flatspec.fixturecontext

import collection.mutable.ListBuffer
import org.scalatest.FlatSpec

class ExampleSpec extends FlatSpec {

  trait Builder {
    val builder = new StringBuilder("ScalaTest is ")
  }

  trait Buffer {
    val buffer = ListBuffer("ScalaTest", "is")
  }

  // This test needs the StringBuilder fixture
  "Testing" should "be productive" in new Builder {
    builder.append("productive!")
    assert(builder.toString === "ScalaTest is productive!")
  }

  // This test needs the ListBuffer[String] fixture
  "Test code" should "be readable" in new Buffer {
    buffer += ("readable!")
    assert(buffer === List("ScalaTest", "is", "readable!"))
  }

  // This test needs both the StringBuilder and ListBuffer
  it should "be clear and concise" in new Builder with Buffer {
    builder.append("clear!")
    buffer += ("concise!")
    assert(builder.toString === "ScalaTest is clear!")
    assert(buffer === List("ScalaTest", "is", "concise!"))
  }
}

Overriding `withFixture(NoArgTest)`

Although the get-fixture method and fixture-context object approaches take care of setting up a fixture at the beginning of each test, they don't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgTest), one of ScalaTest's lifecycle methods defined in trait Suite.

Trait Suite's implementation of runTest passes a no-arg test function to withFixture(NoArgTest). It is withFixture's responsibility to invoke that test function. Suite's implementation of withFixture simply invokes the function, like this:

// Default implementation in trait Suite
protected def withFixture(test: NoArgTest) = {
  test()
}

You can, therefore, override withFixture to perform setup before and/or cleanup after invoking the test function. If you have cleanup to perform, you should invoke the test function inside a try block and perform the cleanup in a finally clause, in case an exception propagates back through withFixture. (If a test fails because of an exception, the test function invoked by withFixture will result in a Failed wrapping the exception. Nevertheless, best practice is to perform cleanup in a finally clause just in case an exception occurs.)

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. That is to say, instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgTest) = {
  // Perform setup
  try super.withFixture(test) // Invoke the test function
  finally {
    // Perform cleanup
  }
}

Here's an example in which withFixture(NoArgTest) is used to take a snapshot of the working directory if a test fails, and send that information to the reporter:

package org.scalatest.examples.flatspec.noargtest

import java.io.File
import org.scalatest._

class ExampleSpec extends FlatSpec {

  override def withFixture(test: NoArgTest) = {

    super.withFixture(test) match {
      case failed: Failed =>
        val currDir = new File(".")
        val fileNames = currDir.list()
        info("Dir snapshot: " + fileNames.mkString(", "))
        failed
      case other => other
    }
  }

  "This test" should "succeed" in {
    assert(1 + 1 === 2)
  }

  it should "fail" in {
    assert(1 + 1 === 3)
  }
}

Running this version of ExampleSuite in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSuite)
ExampleSuite:
This test
- should succeed
- should fail *** FAILED ***
  2 did not equal 3 (:33)
  + Dir snapshot: hello.txt, world.txt

Note that the NoArgTest passed to withFixture, in addition to an apply method that executes the test, also includes TestData such as the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

package org.scalatest.examples.flatspec.loanfixture

import java.util.concurrent.ConcurrentHashMap

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer
    databases.put(name, db)
    db
  }
  def removeDb(name: String) {
    databases.remove(name)
  }
}

import org.scalatest.FlatSpec
import DbServer._
import java.util.UUID.randomUUID
import java.io._

class ExampleSpec extends FlatSpec {

  def withDatabase(testCode: Db => Any) {
    val dbName = randomUUID.toString
    val db = createDb(dbName) // create the fixture
    try {
      db.append("ScalaTest is ") // perform setup
      testCode(db) // "loan" the fixture to the test
    }
    finally removeDb(dbName) // clean up the fixture
  }

  def withFile(testCode: (File, FileWriter) => Any) {
    val file = File.createTempFile("hello", "world") // create the fixture
    val writer = new FileWriter(file)
    try {
      writer.write("ScalaTest is ") // set up the fixture
      testCode(file, writer) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  // This test needs the file fixture
  "Testing" should "be productive" in withFile { (file, writer) =>
    writer.write("productive!")
    writer.flush()
    assert(file.length === 24)
  }

  // This test needs the database fixture
  "Test code" should "be readable" in withDatabase { db =>
    db.append("readable!")
    assert(db.toString === "ScalaTest is readable!")
  }

  // This test needs both the file and the database
  it should "be clear and concise" in withDatabase { db =>
    withFile { (file, writer) => // loan-fixture methods compose
      db.append("clear!")
      writer.write("concise!")
      writer.flush()
      assert(db.toString === "ScalaTest is clear!")
      assert(file.length === 21)
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating files or databases, it is a good idea to give each file or database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.FlatSpec and overriding withFixture(OneArgTest). Each test in a fixture.FlatSpec takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgTest. This withFixture method is responsible for invoking the one-arg test function, so you can perform fixture set up before, and clean up after, invoking and passing the fixture into the test function.

To enable the stacking of traits that define withFixture(NoArgTest), it is a good idea to let withFixture(NoArgTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgTest to a NoArgTest. You can do that by passing the fixture object to the toNoArgTest method of OneArgTest. In other words, instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgTest) method of the same instance by writing:

withFixture(test.toNoArgTest(theFixture))

Here's a complete example:

package org.scalatest.examples.flatspec.oneargtest

import org.scalatest.fixture
import java.io._

class ExampleSpec extends fixture.FlatSpec {

  case class FixtureParam(file: File, writer: FileWriter)

  def withFixture(test: OneArgTest) = {
    val file = File.createTempFile("hello", "world") // create the fixture
    val writer = new FileWriter(file)
    val theFixture = FixtureParam(file, writer)

    try {
      writer.write("ScalaTest is ") // set up the fixture
      withFixture(test.toNoArgTest(theFixture)) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  "Testing" should "be easy" in { f =>
    f.writer.write("easy!")
    f.writer.flush()
    assert(f.file.length === 18)
  }

  it should "be fun" in { f =>
    f.writer.write("fun!")
    f.writer.flush()
    assert(f.file.length === 17)
  }
}

In this example, the tests actually required two fixture objects, a File and a FileWriter. In such situations you can simply define the FixtureParam type to be a tuple containing the objects, or as is done in this example, a case class containing the objects. For more information on the withFixture(OneArgTest) technique, see the documentation for fixture.FlatSpec.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.flatspec.beforeandafter

import org.scalatest._
import collection.mutable.ListBuffer

class ExampleSpec extends FlatSpec with BeforeAndAfter {

  val builder = new StringBuilder
  val buffer = new ListBuffer[String]

  before {
    builder.append("ScalaTest is ")
  }

  after {
    builder.clear()
    buffer.clear()
  }

  "Testing" should "be easy" in {
    builder.append("easy!")
    assert(builder.toString === "ScalaTest is easy!")
    assert(buffer.isEmpty)
    buffer += "sweet"
  }

  it should "be fun" in {
    builder.append("fun!")
    assert(builder.toString === "ScalaTest is fun!")
    assert(buffer.isEmpty)
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state. This is why ScalaTest's ParallelTestExecution trait extends OneInstancePerTest. By running each test in its own instance of the class, each test has its own copy of the instance variables, so you don't need to synchronize. If you mixed ParallelTestExecution into the ExampleSuite above, the tests would run in parallel just fine without any synchronization needed on the mutable StringBuilder and ListBuffer[String] objects.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilder and ListBuffer[String] fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.flatspec.composingwithfixture

import org.scalatest._
import collection.mutable.ListBuffer

trait Builder extends TestSuiteMixin { this: TestSuite =>

  val builder = new StringBuilder

  abstract override def withFixture(test: NoArgTest) = {
    builder.append("ScalaTest is ")
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally builder.clear()
  }
}

trait Buffer extends TestSuiteMixin { this: TestSuite =>

  val buffer = new ListBuffer[String]

  abstract override def withFixture(test: NoArgTest) = {
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally buffer.clear()
  }
}

class ExampleSpec extends FlatSpec with Builder with Buffer {

  "Testing" should "be easy" in {
    builder.append("easy!")
    assert(builder.toString === "ScalaTest is easy!")
    assert(buffer.isEmpty)
    buffer += "sweet"
  }

  it should "be fun" in {
    builder.append("fun!")
    assert(builder.toString === "ScalaTest is fun!")
    assert(buffer.isEmpty)
    buffer += "clear"
  }
}

By mixing in both the Builder and Buffer traits, ExampleSuite gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Spec extends FlatSpec with Buffer with Builder

And if you only need one fixture you mix in only that trait:

class Example3Spec extends FlatSpec with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.flatspec.composingbeforeandaftereach

import org.scalatest._
import collection.mutable.ListBuffer

trait Builder extends BeforeAndAfterEach { this: Suite =>

  val builder = new StringBuilder

  override def beforeEach() {
    builder.append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builder.clear()
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  val buffer = new ListBuffer[String]

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally buffer.clear()
  }
}

class ExampleSpec extends FlatSpec with Builder with Buffer {

  "Testing" should "be easy" in {
    builder.append("easy!")
    assert(builder.toString === "ScalaTest is easy!")
    assert(buffer.isEmpty)
    buffer += "sweet"
  }

  it should "be fun" in {
    builder.append("fun!")
    assert(builder.toString === "ScalaTest is fun!")
    assert(buffer.isEmpty)
    buffer += "clear"
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in a FlatSpec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any FlatSpec that uses them, so that the tests they contain will be registered as tests in that FlatSpec. For example, given this stack class:

import scala.collection.mutable.ListBuffer

class Stack[T] {

  val MAX = 10
  private val buf = new ListBuffer[T]

  def push(o: T) {
    if (!full)
      buf.prepend(o)
    else
      throw new IllegalStateException("can't push onto a full stack")
  }

  def pop(): T = {
    if (!empty)
      buf.remove(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def peek: T = {
    if (!empty)
      buf(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def full: Boolean = buf.size == MAX
  def empty: Boolean = buf.size == 0
  def size = buf.size

  override def toString = buf.mkString("Stack(", ", ", ")")
}

You may want to test the Stack class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several tests that make sense any time the stack is non-empty. Thus you'd ideally want to run those same tests for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these tests out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your FlatSpec for stack, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared tests are run for all three fixtures. You can define a behavior function that encapsulates these shared tests inside the FlatSpec that uses them. If they are shared between different FlatSpecs, however, you could also define them in a separate trait that is mixed into each FlatSpec that uses them.

For example, here the nonEmptyStack behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared tests for non-full stacks:

trait StackBehaviors { this: FlatSpec =>

  def nonEmptyStack(newStack: => Stack[Int], lastItemAdded: Int) {

    it should "be non-empty" in {
      assert(!newStack.empty)
    }

    it should "return the top item on peek" in {
      assert(newStack.peek === lastItemAdded)
    }

    it should "not remove the top item on peek" in {
      val stack = newStack
      val size = stack.size
      assert(stack.peek === lastItemAdded)
      assert(stack.size === size)
    }

    it should "remove the top item on pop" in {
      val stack = newStack
      val size = stack.size
      assert(stack.pop === lastItemAdded)
      assert(stack.size === size - 1)
    }
  }

  def nonFullStack(newStack: => Stack[Int]) {

    it should "not be full" in {
      assert(!newStack.full)
    }

    it should "add to the top on push" in {
      val stack = newStack
      val size = stack.size
      stack.push(7)
      assert(stack.size === size + 1)
      assert(stack.peek === 7)
    }
  }
}

Given these behavior functions, you could invoke them directly, but FlatSpec offers a DSL for the purpose, which looks like this:

it should behave like nonEmptyStack(stackWithOneItem, lastValuePushed)
it should behave like nonFullStack(stackWithOneItem)

If you prefer to use an imperative style to change fixtures, for example by mixing in BeforeAndAfterEach and reassigning a stack var in beforeEach, you could write your behavior functions in the context of that var, which means you wouldn't need to pass in the stack fixture because it would be in scope already inside the behavior function. In that case, your code would look like this:

it should behave like nonEmptyStack // assuming lastValuePushed is also in scope inside nonEmptyStack
it should behave like nonFullStack

The recommended style, however, is the functional, pass-all-the-needed-values-in style. Here's an example:

class SharedTestExampleSpec extends FlatSpec with StackBehaviors {

  // Stack fixture creation methods
  def emptyStack = new Stack[Int]

  def fullStack = {
    val stack = new Stack[Int]
    for (i <- 0 until stack.MAX)
      stack.push(i)
    stack
  }

  def stackWithOneItem = {
    val stack = new Stack[Int]
    stack.push(9)
    stack
  }

  def stackWithOneItemLessThanCapacity = {
    val stack = new Stack[Int]
    for (i <- 1 to 9)
      stack.push(i)
    stack
  }

  val lastValuePushed = 9

  "A Stack (when empty)" should "be empty" in {
    assert(emptyStack.empty)
  }

  it should "complain on peek" in {
    assertThrows[IllegalStateException] {
      emptyStack.peek
    }
  }

  it should "complain on pop" in {
    assertThrows[IllegalStateException] {
      emptyStack.pop
    }
  }

  "A Stack (with one item)" should behave like nonEmptyStack(stackWithOneItem, lastValuePushed)

  it should behave like nonFullStack(stackWithOneItem)

  "A Stack (with one item less than capacity)" should behave like nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed)

  it should behave like nonFullStack(stackWithOneItemLessThanCapacity)

  "A Stack (full)" should "be full" in {
    assert(fullStack.full)
  }

  it should behave like nonEmptyStack(fullStack, lastValuePushed)

  it should "complain on a push" in {
    assertThrows[IllegalStateException] {
      fullStack.push(10)
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> org.scalatest.run(new SharedTestExampleSpec)
A Stack (when empty)
- should be empty
- should complain on peek
- should complain on pop
A Stack (with one item)
- should be non-empty
- should return the top item on peek
- should not remove the top item on peek
- should remove the top item on pop
- should not be full
- should add to the top on push
A Stack (with one item less than capacity)
- should be non-empty
- should return the top item on peek
- should not remove the top item on peek
- should remove the top item on pop
- should not be full
- should add to the top on push
A Stack (full)
- should be full
- should be non-empty
- should return the top item on peek
- should not remove the top item on peek
- should remove the top item on pop
- should complain on a push

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. A good way to solve this problem in a FlatSpec is to make sure each invocation of a behavior function is in the context of a different set of when, verb (should, must, or can), and that clauses, which will prepend a string to each test name. For example, the following code in a FlatSpec would register a test with the name "A Stack (when empty) should be empty":

behavior of "A Stack (when empty)"

it should "be empty" in {
  assert(emptyStack.empty)
}
// ...

Or, using the shorthand notation:

"A Stack" when {
  "empty" should {
    "be empty" in {
      assert(emptyStack.empty)
    }
  }
}
// ...

If the "should be empty" test was factored out into a behavior function, it could be called repeatedly so long as each invocation of the behavior function is in the context of a different combination of when, verb, and that clauses.

trait FlatSpecLike extends TestSuite with TestRegistration with ShouldVerb with MustVerb with CanVerb with Informing with Notifying with Alerting with Documenting

Implementation trait for class FlatSpec, which facilitates a “behavior-driven” style of development (BDD), in which tests are combined with text that specifies the behavior the tests verify.

FlatSpec is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of FlatSpec into some other class, you can use this trait instead, because class FlatSpec does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of FlatSpec.

class FreeSpec extends FreeSpecLike

Facilitates a “behavior-driven” style of development (BDD), in which tests are nested inside text clauses denoted with the dash operator (-).

FreeSpec is so named because unlike classes such as WordSpec, FlatSpec, and FunSpec, it is enforces no structure on the text. You are free to compose text however you like. (A FreeSpec is like free-verse poetry as opposed to a sonnet or haiku, which defines a structure for the text of the poem.)

Recommended Usage: Because it gives absolute freedom (and no guidance) on how specification text should be written, FreeSpec is a good choice for teams experienced with BDD and able to agree on how to structure the specification text.

Here's an example FreeSpec:

package org.scalatest.examples.freespec

import org.scalatest.FreeSpec

class SetSpec extends FreeSpec {

  "A Set" - {
    "when empty" - {
      "should have size 0" in {
        assert(Set.empty.size === 0)
      }

      "should produce NoSuchElementException when head is invoked" in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

In a FreeSpec you write a test with a string followed by in and the body of the test in curly braces, like this:

"should have size 0" in {
  // ...
}

You can nest a test inside any number of description clauses, which you write with a string followed by a dash character and a block, like this:

"A Set" - {
  // ...
}

You can nest description clauses as deeply as you want. Because the description clause is denoted with an operator, not a word like should, you are free to structure the text however you wish. Here's an example:

import org.scalatest.FreeSpec

class StackSpec extends FreeSpec {
  "A Stack" - {
    "whenever it is empty" - {
      "certainly ought to" - {
        "be empty" in {
          // ...
        }
        "complain on peek" in {
          // ...
        }
        "complain on pop" in {
          // ...
        }
      }
    }
    "but when full, by contrast, must" - {
      "be full" in {
        // ...
      }
      "complain on push" in {
        // ...
      }
    }
  }
}

Running the above StackSpec in the interpreter would yield:

scala> org.scalatest.run(new StackSpec)
StackSpec:
A Stack
  whenever it is empty
    certainly ought to
    - be empty
    - complain on peek
    - complain on pop
  but when full, by contrast, must
  - be full
  - complain on push

A FreeSpec can also be used to write a specification-style test in languages other than English. For example:

import org.scalatest.FreeSpec

class ComputerRoomRulesSpec extends FreeSpec {
  "Achtung!" - {
    "Alle touristen und non-technischen lookenpeepers!" - {
      "Das machine is nicht fuer fingerpoken und mittengrabben." in {
        // ...
      }
      "Is easy" - {
        "schnappen der springenwerk" in {
          // ...
        }
        "blowenfusen" in {
          // ...
        }
        "und poppencorken mit spitzen sparken." in {
          // ...
        }
      }
      "Das machine is diggen by experten only." in {
        // ...
      }
      "Is nicht fuer gerwerken by das dummkopfen." in {
        // ...
      }
      "Das rubbernecken sightseeren keepen das cottenpicken hands in das pockets." in {
        // ...
      }
      "Relaxen und watchen das blinkenlights." in {
        // ...
      }
    }
  }
}

Running the above ComputerRoomRulesSpec in the interpreter would yield:

scala> org.scalatest.run(new ComputerRoomRulesSpec)
ComputerRoomRulesSpec:
Achtung!
  Alle touristen und non-technischen lookenpeepers!
  - Das machine is nicht fuer fingerpoken und mittengrabben.
    Is easy
    - schnappen der springenwerk
    - blowenfusen
    - und poppencorken mit spitzen sparken.
  - Das machine is diggen by experten only.
  - Is nicht fuer gerwerken by das dummkopfen.
  - Das rubbernecken sightseeren keepen das cottenpicken hands in das pockets.
  - Relaxen und watchen das blinkenlights.

A FreeSpec's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Tests can only be registered while the FreeSpec is in its registration phase. Any attempt to register a test after the FreeSpec has entered its ready phase, i.e., after run has been invoked on the FreeSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using FreeSpec is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, FreeSpec adds a method ignore to strings that can be used instead of in to register a test. For example, to temporarily disable the test with the name "A Stack should pop values in last-in-first-out order", just change “in” into “ignore,” like this:

package org.scalatest.examples.freespec.ignore

import org.scalatest.FreeSpec

class SetSpec extends FreeSpec {

  "A Set" - {
    "when empty" - {
      "should have size 0" ignore {
        assert(Set.empty.size === 0)
      }

      "should produce NoSuchElementException when head is invoked" in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

If you run this version of SetSpec with:

scala> org.scalatest.run(new SetSpec)

It will run only the second test and report that the first test was ignored:

A Set
  when empty
  - should have size 0 !!! IGNORED !!!
  - should produce NoSuchElementException when head is invoked

If you wish to temporarily ignore an entire suite of tests, you can (on the JVM, not Scala.js) annotate the test class with @Ignore, like this:

package org.scalatest.examples.freespec.ignoreall

import org.scalatest.FreeSpec
import org.scalatest.Ignore

@Ignore
class SetSpec extends FreeSpec {

  "A Set" - {
    "when empty" - {
      "should have size 0" in {
        assert(Set.empty.size === 0)
      }

      "should produce NoSuchElementException when head is invoked" in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the SetSpec in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above SetSpec in the Scala interpreter, you'll see:

scala> org.scalatest.run(new SetSpec)
SetSpec:
A Set
  when empty
  - should have size 0 !!! IGNORED !!!
  - should produce NoSuchElementException when head is invoked !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class visible, to encourage the developers to eventually fix and “un-ignore” it. If you want to prevent a class from being discovered at all (on the JVM, not Scala.js), use the DoNotDiscover annotation instead.

Informers

One of the parameters to FreeSpec's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the reporting done by default by FreeSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event.

One use case for the Informer is to pass more information about a specification to the reporter. For example, the GivenWhenThen trait provides methods that use the implicit info provided by FreeSpec to pass such information to the reporter. Here's an example:

package org.scalatest.examples.freespec.info

import collection.mutable
import org.scalatest._

class SetSpec extends FreeSpec with GivenWhenThen {

  "A mutable Set" - {
    "should allow an element to be added" in {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      info("That's all folks!")
    }
  }
}

If you run this FreeSpec from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSpec)
A mutable Set
- should allow an element to be added
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

Documenters

FreeSpec also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example FreeSpec that uses markup:

package org.scalatest.examples.freespec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends FreeSpec with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

    def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  "A mutable Set" - {
    "should allow an element to be added" in {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      markup("This test finished with a **bold** statement!")
    }
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.freespec.note

import collection.mutable
import org.scalatest._

class SetSpec extends FreeSpec {

  "A mutable Set" - {
    "should allow an element to be added" in {

      info("info is recorded")
      markup("markup is *also* recorded")
      note("notes are sent immediately")
      alert("alerts are also sent immediately")

      val set = mutable.Set.empty[String]
      set += "clarity"
      assert(set.size === 1)
      assert(set.contains("clarity"))
    }
  }
}

scala> org.scalatest.run(new SetSpec)
SetSpec:
 A mutable Set
   + notes are sent immediately
   + alerts are also sent immediately
 - should allow an element to be added
   + info is recorded
   + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. The test can also include some code that sends more information about the behavior to the reporter when the tests run. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality it is intended to test, has not yet been implemented. You can mark tests as pending in a FreeSpec like this:

package org.scalatest.examples.freespec.pending

import org.scalatest._

class SetSpec extends FreeSpec {

  "A Set" - {
    "when empty" - {
      "should have size 0" in (pending)

      "should produce NoSuchElementException when head is invoked" in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

If you run this version of SetSpec with:

scala> org.scalatest.run(new SetSpec)

It will run both tests but report that should have size 0 is pending. You'll see:

A Set
  when empty
  - should have size 0 (pending)
  - should produce NoSuchElementException when head is invoked

One difference between an ignored test and a pending one is that an ignored test is intended to be used during a significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException. The reason for this difference is that it enables your unfinished test to send InfoProvided messages to the reporter before it completes abruptly with TestPendingException, as shown in the previous example on Informers that used the GivenWhenThen trait. For example, the following snippet in a FreeSpec:

"The Scala language" - {
   "should add correctly" in {
     Given("two integers")
     When("they are added")
     Then("the result is the sum of the two numbers")
     pending
   }
   // ...

Would yield the following output when run in the interpreter:

The Scala language
- should add correctly (pending)
  + Given two integers
  + When they are added
  + Then the result is the sum of the two numbers

Tagging tests

A FreeSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing a FreeSpec, groups of tests can optionally be included and/or excluded. To tag a FreeSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for FreeSpecs like this:

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could tag FreeSpec tests like this:

package org.scalatest.examples.freespec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

import org.scalatest.FreeSpec
import org.scalatest.tagobjects.Slow

class SetSpec extends FreeSpec {

  "A Set" - {
    "when empty" - {
      "should have size 0" taggedAs(Slow) in {
        assert(Set.empty.size === 0)
      }

      "should produce NoSuchElementException when head is invoked" taggedAs(Slow, DbTest) in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of a FreeSpec in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and more amenable for parallel test execution.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
fixture-context objects	By placing fixture methods and fields into traits, you can easily give each test just the newly created fixtures it needs by mixing together traits. Use this technique when you need different combinations of mutable fixture objects in different tests, and don't need to clean up after.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgTest)` instead)
`withFixture(OneArgTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or an holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.freespec.getfixture

import org.scalatest.FreeSpec
import collection.mutable.ListBuffer

class ExampleSpec extends FreeSpec {

  class Fixture {
    val builder = new StringBuilder("ScalaTest is ")
    val buffer = new ListBuffer[String]
  }

  def fixture = new Fixture

  "Testing" - {
    "should be easy" in {
      val f = fixture
      f.builder.append("easy!")
      assert(f.builder.toString === "ScalaTest is easy!")
      assert(f.buffer.isEmpty)
      f.buffer += "sweet"
    }

    "should be fun" in {
      val f = fixture
      f.builder.append("fun!")
      assert(f.builder.toString === "ScalaTest is fun!")
      assert(f.buffer.isEmpty)
    }
  }
}

The “f.” in front of each use of a fixture object provides a visual indication of which objects are part of the fixture, but if you prefer, you can import the the members with “import f._” and use the names directly.

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, if you could pass in an initial value for a mutable fixture object as a parameter to the get-fixture method.

Instantiating fixture-context objects

An alternate technique that is especially useful when different tests need different combinations of fixture objects is to define the fixture objects as instance variables of fixture-context objects whose instantiation forms the body of tests. Like get-fixture methods, fixture-context objects are only appropriate if you don't need to clean up the fixtures after using them.

To use this technique, you define instance variables intialized with fixture objects in traits and/or classes, then in each test instantiate an object that contains just the fixture objects needed by the test. Traits allow you to mix together just the fixture objects needed by each test, whereas classes allow you to pass data in via a constructor to configure the fixture objects. Here's an example in which fixture objects are partitioned into two traits and each test just mixes together the traits it needs:

package org.scalatest.examples.freespec.fixturecontext

import collection.mutable.ListBuffer
import org.scalatest.FreeSpec

class ExampleSpec extends FreeSpec {

  trait Builder {
    val builder = new StringBuilder("ScalaTest is ")
  }

  trait Buffer {
    val buffer = ListBuffer("ScalaTest", "is")
  }

  "Testing" - {
    // This test needs the StringBuilder fixture
    "should be productive" in new Builder {
      builder.append("productive!")
      assert(builder.toString === "ScalaTest is productive!")
    }
  }

  "Test code" - {
    // This test needs the ListBuffer[String] fixture
    "should be readable" in new Buffer {
      buffer += ("readable!")
      assert(buffer === List("ScalaTest", "is", "readable!"))
    }

    // This test needs both the StringBuilder and ListBuffer
    "should be clear and concise" in new Builder with Buffer {
      builder.append("clear!")
      buffer += ("concise!")
      assert(builder.toString === "ScalaTest is clear!")
      assert(buffer === List("ScalaTest", "is", "concise!"))
    }
  }
}

Overriding `withFixture(NoArgTest)`

Although the get-fixture method and fixture-context object approaches take care of setting up a fixture at the beginning of each test, they don't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgTest), one of ScalaTest's lifecycle methods defined in trait Suite.

Trait Suite's implementation of runTest passes a no-arg test function to withFixture(NoArgTest). It is withFixture's responsibility to invoke that test function. Suite's implementation of withFixture simply invokes the function, like this:

// Default implementation in trait Suite
protected def withFixture(test: NoArgTest) = {
  test()
}

You can, therefore, override withFixture to perform setup before and/or cleanup after invoking the test function. If you have cleanup to perform, you should invoke the test function inside a try block and perform the cleanup in a finally clause, in case an exception propagates back through withFixture. (If a test fails because of an exception, the test function invoked by withFixture will result in a Failed wrapping the exception. Nevertheless, best practice is to perform cleanup in a finally clause just in case an exception occurs.)

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. In other words, instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgTest) = {
  // Perform setup
  try super.withFixture(test) // Invoke the test function
  finally {
    // Perform cleanup
  }
}

Here's an example in which withFixture(NoArgTest) is used to take a snapshot of the working directory if a test fails, and send that information to the reporter:

package org.scalatest.examples.freespec.noargtest

import java.io.File
import org.scalatest._

class ExampleSpec extends FreeSpec {

  override def withFixture(test: NoArgTest) = {

    super.withFixture(test) match {
      case failed: Failed =>
        val currDir = new File(".")
        val fileNames = currDir.list()
        info("Dir snapshot: " + fileNames.mkString(", "))
        failed
      case other => other
    }
  }

  "This test" - {
    "should succeed" in {
      assert(1 + 1 === 2)
    }

    "should fail" in {
      assert(1 + 1 === 3)
    }
  }
}

Running this version of ExampleSuite in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSuite)
ExampleSuite:
This test
- should succeed
- should fail *** FAILED ***
  2 did not equal 3 (:33)
  + Dir snapshot: hello.txt, world.txt

Note that the NoArgTest passed to withFixture, in addition to an apply method that executes the test, also includes the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

package org.scalatest.examples.freespec.loanfixture

import java.util.concurrent.ConcurrentHashMap

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer
    databases.put(name, db)
    db
  }
  def removeDb(name: String) {
    databases.remove(name)
  }
}

import org.scalatest.FreeSpec
import DbServer._
import java.util.UUID.randomUUID
import java.io._

class ExampleSpec extends FreeSpec {

  def withDatabase(testCode: Db => Any) {
    val dbName = randomUUID.toString
    val db = createDb(dbName) // create the fixture
    try {
      db.append("ScalaTest is ") // perform setup
      testCode(db) // "loan" the fixture to the test
    }
    finally removeDb(dbName) // clean up the fixture
  }

  def withFile(testCode: (File, FileWriter) => Any) {
    val file = File.createTempFile("hello", "world") // create the fixture
    val writer = new FileWriter(file)
    try {
      writer.write("ScalaTest is ") // set up the fixture
      testCode(file, writer) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  "Testing" - {
    // This test needs the file fixture
    "should be productive" in withFile { (file, writer) =>
      writer.write("productive!")
      writer.flush()
      assert(file.length === 24)
    }
  }

  "Test code" - {
    // This test needs the database fixture
    "should be readable" in withDatabase { db =>
      db.append("readable!")
      assert(db.toString === "ScalaTest is readable!")
    }

    // This test needs both the file and the database
    "should be clear and concise" in withDatabase { db =>
      withFile { (file, writer) => // loan-fixture methods compose
        db.append("clear!")
        writer.write("concise!")
        writer.flush()
        assert(db.toString === "ScalaTest is clear!")
        assert(file.length === 21)
      }
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating files or databases, it is a good idea to give each file or database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.FreeSpec and overriding withFixture(OneArgTest). Each test in a fixture.FreeSpec takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgTest. This withFixture method is responsible for invoking the one-arg test function, so you can perform fixture set up before, and clean up after, invoking and passing the fixture into the test function.

To enable the stacking of traits that define withFixture(NoArgTest), it is a good idea to let withFixture(NoArgTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgTest to a NoArgTest. You can do that by passing the fixture object to the toNoArgTest method of OneArgTest. In other words, instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgTest) method of the same instance by writing:

withFixture(test.toNoArgTest(theFixture))

Here's a complete example:

package org.scalatest.examples.freespec.oneargtest

import org.scalatest.fixture
import java.io._

class ExampleSpec extends fixture.FreeSpec {

  case class FixtureParam(file: File, writer: FileWriter)

  def withFixture(test: OneArgTest) = {

    // create the fixture
    val file = File.createTempFile("hello", "world")
    val writer = new FileWriter(file)
    val theFixture = FixtureParam(file, writer)

    try {
      writer.write("ScalaTest is ") // set up the fixture
      withFixture(test.toNoArgTest(theFixture)) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  "Testing" - {
    "should be easy" in { f =>
      f.writer.write("easy!")
      f.writer.flush()
      assert(f.file.length === 18)
    }

    "should be fun" in { f =>
      f.writer.write("fun!")
      f.writer.flush()
      assert(f.file.length === 17)
    }
  }
}

In this example, the tests actually required two fixture objects, a File and a FileWriter. In such situations you can simply define the FixtureParam type to be a tuple containing the objects, or as is done in this example, a case class containing the objects. For more information on the withFixture(OneArgTest) technique, see the documentation for fixture.FreeSpec.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.freespec.beforeandafter

import org.scalatest.FreeSpec
import org.scalatest.BeforeAndAfter
import collection.mutable.ListBuffer

class ExampleSpec extends FreeSpec with BeforeAndAfter {

  val builder = new StringBuilder
  val buffer = new ListBuffer[String]

  before {
    builder.append("ScalaTest is ")
  }

  after {
    builder.clear()
    buffer.clear()
  }

  "Testing" - {
    "should be easy" in {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    "should be fun" in {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
    }
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state. This is why ScalaTest's ParallelTestExecution trait extends OneInstancePerTest. By running each test in its own instance of the class, each test has its own copy of the instance variables, so you don't need to synchronize. If you mixed ParallelTestExecution into the ExampleSuite above, the tests would run in parallel just fine without any synchronization needed on the mutable StringBuilder and ListBuffer[String] objects.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilder and ListBuffer[String] fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.freespec.composingwithfixture

import org.scalatest._
import collection.mutable.ListBuffer

trait Builder extends TestSuiteMixin { this: TestSuite =>

  val builder = new StringBuilder

  abstract override def withFixture(test: NoArgTest) = {
    builder.append("ScalaTest is ")
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally builder.clear()
  }
}

trait Buffer extends TestSuiteMixin { this: TestSuite =>

  val buffer = new ListBuffer[String]

  abstract override def withFixture(test: NoArgTest) = {
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally buffer.clear()
  }
}

class ExampleSpec extends FreeSpec with Builder with Buffer {

  "Testing" - {
    "should be easy" in {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    "should be fun" in {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }
  }
}

By mixing in both the Builder and Buffer traits, ExampleSuite gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Spec extends FreeSpec with Buffer with Builder

And if you only need one fixture you mix in only that trait:

class Example3Spec extends FreeSpec with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.freespec.composingbeforeandaftereach

import org.scalatest._
import org.scalatest.BeforeAndAfterEach
import collection.mutable.ListBuffer

trait Builder extends BeforeAndAfterEach { this: Suite =>

  val builder = new StringBuilder

  override def beforeEach() {
    builder.append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builder.clear()
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  val buffer = new ListBuffer[String]

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally buffer.clear()
  }
}

class ExampleSpec extends FreeSpec with Builder with Buffer {

  "Testing" - {
    "should be easy" in {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    "should be fun" in {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in a FreeSpec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any FreeSpec that uses them, so that the tests they contain will be registered as tests in that FreeSpec. For example, given this stack class:

import scala.collection.mutable.ListBuffer

class Stack[T] {

  val MAX = 10
  private val buf = new ListBuffer[T]

  def push(o: T) {
    if (!full)
      buf.prepend(o)
    else
      throw new IllegalStateException("can't push onto a full stack")
  }

  def pop(): T = {
    if (!empty)
      buf.remove(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def peek: T = {
    if (!empty)
      buf(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def full: Boolean = buf.size == MAX
  def empty: Boolean = buf.size == 0
  def size = buf.size

  override def toString = buf.mkString("Stack(", ", ", ")")
}

You may want to test the Stack class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several tests that make sense any time the stack is non-empty. Thus you'd ideally want to run those same tests for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these tests out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your FreeSpec for stack, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared tests are run for all three fixtures. You can define a behavior function that encapsulates these shared tests inside the FreeSpec that uses them. If they are shared between different FreeSpecs, however, you could also define them in a separate trait that is mixed into each FreeSpec that uses them.

For example, here the nonEmptyStack behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared tests for non-full stacks:

trait StackBehaviors { this: FreeSpec =>

  def nonEmptyStack(newStack: => Stack[Int], lastItemAdded: Int) {

    "be non-empty" in {
      assert(!newStack.empty)
    }

    "return the top item on peek" in {
      assert(newStack.peek === lastItemAdded)
    }

    "not remove the top item on peek" in {
      val stack = newStack
      val size = stack.size
      assert(stack.peek === lastItemAdded)
      assert(stack.size === size)
    }

    "remove the top item on pop" in {
      val stack = newStack
      val size = stack.size
      assert(stack.pop === lastItemAdded)
      assert(stack.size === size - 1)
    }
  }

  def nonFullStack(newStack: => Stack[Int]) {

    "not be full" in {
      assert(!newStack.full)
    }

    "add to the top on push" in {
      val stack = newStack
      val size = stack.size
      stack.push(7)
      assert(stack.size === size + 1)
      assert(stack.peek === 7)
    }
  }
}

Given these behavior functions, you could invoke them directly, but FreeSpec offers a DSL for the purpose, which looks like this:

behave like nonEmptyStack(stackWithOneItem, lastValuePushed)
behave like nonFullStack(stackWithOneItem)

If you prefer to use an imperative style to change fixtures, for example by mixing in BeforeAndAfterEach and reassigning a stack var in beforeEach, you could write your behavior functions in the context of that var, which means you wouldn't need to pass in the stack fixture because it would be in scope already inside the behavior function. In that case, your code would look like this:

behave like nonEmptyStack // assuming lastValuePushed is also in scope inside nonEmptyStack
behave like nonFullStack

The recommended style, however, is the functional, pass-all-the-needed-values-in style. Here's an example:

class SharedTestExampleSpec extends FreeSpec with StackBehaviors {

  // Stack fixture creation methods
  def emptyStack = new Stack[Int]

  def fullStack = {
    val stack = new Stack[Int]
    for (i <- 0 until stack.MAX)
      stack.push(i)
    stack
  }

  def stackWithOneItem = {
    val stack = new Stack[Int]
    stack.push(9)
    stack
  }

  def stackWithOneItemLessThanCapacity = {
    val stack = new Stack[Int]
    for (i <- 1 to 9)
      stack.push(i)
    stack
  }

  val lastValuePushed = 9

  "A Stack" - {
    "when empty" - {
      "should be empty" in {
        assert(emptyStack.empty)
      }

      "should complain on peek" in {
        assertThrows[IllegalStateException] {
          emptyStack.peek
        }
      }

      "should complain on pop" in {
        assertThrows[IllegalStateException] {
          emptyStack.pop
        }
      }
    }

    "when it contains one item" - {
      "should" - {
        behave like nonEmptyStack(stackWithOneItem, lastValuePushed)
        behave like nonFullStack(stackWithOneItem)
      }
    }

    "when it contains one item less than capacity" - {
      "should" - {
        behave like nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed)
        behave like nonFullStack(stackWithOneItemLessThanCapacity)
      }
    }

    "when full" - {
      "should be full" in {
        assert(fullStack.full)
      }

      "should" - {
        behave like nonEmptyStack(fullStack, lastValuePushed)
      }

      "should complain on a push" in {
        assertThrows[IllegalStateException] {
          fullStack.push(10)
        }
      }
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> org.scalatest.run(new SharedTestExampleSpec)
SharedTestExampleSpec:
A Stack
  when empty
  - should be empty
  - should complain on peek
  - should complain on pop
  when it contains one item
    should
    - be non-empty
    - return the top item on peek
    - not remove the top item on peek
    - remove the top item on pop
    - not be full
    - add to the top on push
  when it contains one item less than capacity
    should
    - be non-empty
    - return the top item on peek
    - not remove the top item on peek
    - remove the top item on pop
    - not be full
    - add to the top on push
  when full
  - should be full
    should
    - be non-empty
    - return the top item on peek
    - not remove the top item on peek
    - remove the top item on pop
  - should complain on a push

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. A good way to solve this problem in a FreeSpec is to make sure each test is in the context of different surrounding description clauses, because a test's name is the concatenation of its surrounding clauses, followed by the test's text. For example, the following code in a FreeSpec would register a test with the name "A Stack when empty should be empty":

"A Stack" - {
  "when empty" - {
    "should be empty" in {
      assert(emptyStack.empty)
    }
  }
}
// ...

If the "should be empty" test was factored out into a behavior function, it could be called repeatedly so long as each invocation of the behavior function is in the context of a different surrounding description (dash) clauses.

trait FreeSpecLike extends TestSuite with TestRegistration with Informing with Notifying with Alerting with Documenting

Implementation trait for class FreeSpec, which facilitates a “behavior-driven” style of development (BDD), in which tests are nested inside text clauses denoted with the dash operator (-).

FreeSpec is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of FreeSpec into some other class, you can use this trait instead, because class FreeSpec does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of FreeSpec.

class FunSpec extends FunSpecLike

Facilitates a “behavior-driven” style of development (BDD), in which tests are combined with text that specifies the behavior the tests verify.

Recommended Usage: For teams coming from Ruby's RSpec tool, FunSpec will feel familiar and comfortable; More generally, for any team that prefers BDD, FunSpec's nesting and gentle guide to structuring text (with describe and it) provide an excellent general-purpose choice for writing specification-style tests.

Here's an example FunSpec:

package org.scalatest.examples.funspec

import org.scalatest.FunSpec

class SetSpec extends FunSpec {

  describe("A Set") {
    describe("when empty") {
      it("should have size 0") {
        assert(Set.empty.size === 0)
      }

      it("should produce NoSuchElementException when head is invoked") {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

A FunSpec contains describe clauses and tests. You define a describe clause with describe, and a test with either it or they. describe, it, and they are methods, defined in FunSpec, which will be invoked by the primary constructor of SetSpec. A describe clause names, or gives more information about, the subject (class or other entity) you are specifying and testing. In the previous example, "A Set" is the subject under specification and test. With each test you provide a string (the spec text) that specifies one bit of behavior of the subject, and a block of code that tests that behavior. You place the spec text between the parentheses, followed by the test code between curly braces. The test code will be wrapped up as a function passed as a by-name parameter to it (or they), which will register the test for later execution.

Note: the they method is intended for use when the subject is plural, for example:

describe("The combinators") {
  they("should be easy to learn") {}
  they("should be efficient") {}
  they("should do something cool") {}
}

A FunSpec's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Tests can only be registered with the it or they methods while the FunSpec is in its registration phase. Any attempt to register a test after the FunSpec has entered its ready phase, i.e., after run has been invoked on the FunSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using FunSpec is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

When you execute a FunSpec, it will send Formatters in the events it sends to the Reporter. ScalaTest's built-in reporters will report these events in such a way that the output is easy to read as an informal specification of the subject being tested. For example, were you to run SetSpec from within the Scala interpreter:

scala> org.scalatest.run(new SetSpec)

You would see:

A Set
  when empty
  - should have size 0
  - should produce NoSuchElementException when head is invoked

Or, to run just the “A Set when empty should have size 0” test, you could pass that test's name, or any unique substring of the name, such as "size 0" or even just "0". Here's an example:

scala> org.scalatest.run(new SetSuite, "size 0")
A Set
  when empty
  - should have size 0

You can also pass to execute a config map of key-value pairs, which will be passed down into suites and tests, as well as other parameters that configure the run itself. For more information on running in the Scala interpreter, see the documentation for execute (below) and the ScalaTest shell.

The execute method invokes a run method that takes two parameters. This run method, which actually executes the suite, will usually be invoked by a test runner, such as run, tools.Runner, a build tool, or an IDE.

Note: FunSpec's syntax is in great part inspired by RSpec, a Ruby BDD framework.

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, FunSpec provides registration methods that start with ignore instead of it or they. For example, to temporarily disable the test with the text "should have size 0", just change “it” into “ignore,” like this:

package org.scalatest.examples.funspec.ignore

import org.scalatest.FunSpec

class SetSpec extends FunSpec {

  describe("A Set") {
    describe("when empty") {
      ignore("should have size 0") {
        assert(Set.empty.size === 0)
      }

      it("should produce NoSuchElementException when head is invoked") {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

If you run this version of SetSpec with:

scala> org.scalatest.run(new SetSpec)

It will run only the second test and report that the first test was ignored:

A Set
  when empty
  - should have size 0 !!! IGNORED !!!
  - should produce NoSuchElementException when head is invoked

If you wish to temporarily ignore an entire suite of tests, you can (on the JVM, not Scala.js) annotate the test class with @Ignore, like this:

package org.scalatest.examples.funspec.ignoreall

import org.scalatest.FunSpec
import org.scalatest.Ignore

@Ignore
class SetSpec extends FunSpec {

  describe("A Set") {
    describe("when empty") {
      it("should have size 0") {
        assert(Set.empty.size === 0)
      }

      it("should produce NoSuchElementException when head is invoked") {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the SetSpec in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above SetSpec in the Scala interpreter, you'll see:

scala> org.scalatest.run(new SetSpec)
SetSpec:
A Set
  when empty
  - should have size 0 !!! IGNORED !!!
  - should produce NoSuchElementException when head is invoked !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class visible, to encourage the developers to eventually fix and “un-ignore” it. If you want to prevent a class from being discovered at all (on the JVM, not Scala.js), use the DoNotDiscover annotation instead.

Informers

One of the parameters to FunSpec's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the reporting done by default by FunSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via one of its apply methods. The Informer will then pass the information to the Reporter via an InfoProvided event. Here's an example in which the Informer returned by info is used implicitly by the Given, When, and Then methods of trait GivenWhenThen:

package org.scalatest.examples.funspec.info

import collection.mutable
import org.scalatest._

class SetSpec extends FunSpec with GivenWhenThen {

  describe("A mutable Set") {
    it("should allow an element to be added") {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      info("That's all folks!")
    }
  }
}

If you run this FunSpec from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSpec)
A mutable Set
- should allow an element to be added
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

Documenters

FunSpec also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example FunSpec that uses markup:

package org.scalatest.examples.funspec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends FunSpec with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

    def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  describe("A mutable Set") {
    it("should allow an element to be added") {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      markup("This test finished with a **bold** statement!")
    }
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.funspec.note

import collection.mutable
import org.scalatest._

class SetSpec extends FunSpec {

  describe("A mutable Set") {
    it("should allow an element to be added") {

      info("info is recorded")
      markup("markup is *also* recorded")
      note("notes are sent immediately")
      alert("alerts are also sent immediately")

      val set = mutable.Set.empty[String]
      set += "clarity"
      assert(set.size === 1)
      assert(set.contains("clarity"))
    }
  }
}

Because note and alert information is sent immediately, it will appear before the test name in string reporters, and its color will be unrelated to the ultimate outcome of the test: note text will always appear in green, alert text will always appear in yellow. Here's an example:

scala> org.scalatest.run(new SetSpec)
SetSpec:
A mutable Set
  + notes are sent immediately
  + alerts are also sent immediately
- should allow an element to be added
  + info is recorded
  + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. The test can also include some code that sends more information about the behavior to the reporter when the tests run. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality, has not yet been implemented.

You can mark a test as pending in FunSpec by placing "(pending)" after the test name, like this:

package org.scalatest.examples.funspec.pending

import org.scalatest._

class SetSpec extends FunSpec {

  describe("A Set") {
    describe("when empty") {
      it("should have size 0") (pending)

      it("should produce NoSuchElementException when head is invoked") {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

(Note: "(pending)" is the body of the test. Thus the test contains just one statement, an invocation of the pending method, which throws TestPendingException.) If you run this version of SetSpec with:

scala> org.scalatest.run(new SetSpec)

It will run both tests, but report that the test named "should have size 0" is pending. You'll see:

A Set
  when empty
  - should have size 0 (pending)
  - should produce NoSuchElementException when head is invoked

Tagging tests

A FunSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing a FunSpec, groups of tests can optionally be included and/or excluded. To tag a FunSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for FunSpecs like this:

package org.scalatest.examples.funspec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place FunSpec tests into groups with tags like this:

import org.scalatest.FunSpec
import org.scalatest.tagobjects.Slow

class SetSpec extends FunSpec {

  describe("A Set") {
    describe("when empty") {
      it("should have size 0", Slow) {
        assert(Set.empty.size === 0)
      }

      it("should produce NoSuchElementException when head is invoked", Slow, DbTest) {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of a FunSpec in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and more amenable for parallel test execution.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
fixture-context objects	By placing fixture methods and fields into traits, you can easily give each test just the newly created fixtures it needs by mixing together traits. Use this technique when you need different combinations of mutable fixture objects in different tests, and don't need to clean up after.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgTest)` instead)
`withFixture(OneArgTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or an holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.funspec.getfixture

import org.scalatest.FunSpec
import collection.mutable.ListBuffer

class ExampleSpec extends FunSpec {

  class Fixture {
    val builder = new StringBuilder("ScalaTest is ")
    val buffer = new ListBuffer[String]
  }

  def fixture = new Fixture

  describe("Testing") {
    it("should be easy") {
      val f = fixture
      f.builder.append("easy!")
      assert(f.builder.toString === "ScalaTest is easy!")
      assert(f.buffer.isEmpty)
      f.buffer += "sweet"
    }

    it("should be fun") {
      val f = fixture
      f.builder.append("fun!")
      assert(f.builder.toString === "ScalaTest is fun!")
      assert(f.buffer.isEmpty)
    }
  }
}

The “f.” in front of each use of a fixture object provides a visual indication of which objects are part of the fixture, but if you prefer, you can import the the members with “import f._” and use the names directly.

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, if you could pass in an initial value for a mutable fixture object as a parameter to the get-fixture method.

Instantiating fixture-context objects

An alternate technique that is especially useful when different tests need different combinations of fixture objects is to define the fixture objects as instance variables of fixture-context objects whose instantiation forms the body of tests. Like get-fixture methods, fixture-context objects are only appropriate if you don't need to clean up the fixtures after using them.

To use this technique, you define instance variables intialized with fixture objects in traits and/or classes, then in each test instantiate an object that contains just the fixture objects needed by the test. Traits allow you to mix together just the fixture objects needed by each test, whereas classes allow you to pass data in via a constructor to configure the fixture objects. Here's an example in which fixture objects are partitioned into two traits and each test just mixes together the traits it needs:

package org.scalatest.examples.funspec.fixturecontext

import collection.mutable.ListBuffer
import org.scalatest.FunSpec

class ExampleSpec extends FunSpec {

  trait Builder {
    val builder = new StringBuilder("ScalaTest is ")
  }

  trait Buffer {
    val buffer = ListBuffer("ScalaTest", "is")
  }

  describe("Testing") {
    // This test needs the StringBuilder fixture
    it("should be productive") {
      new Builder {
        builder.append("productive!")
        assert(builder.toString === "ScalaTest is productive!")
      }
    }
  }

  describe("Test code") {
    // This test needs the ListBuffer[String] fixture
    it("should be readable") {
      new Buffer {
        buffer += ("readable!")
        assert(buffer === List("ScalaTest", "is", "readable!"))
      }
    }

    // This test needs both the StringBuilder and ListBuffer
    it("should be clear and concise") {
      new Builder with Buffer {
        builder.append("clear!")
        buffer += ("concise!")
        assert(builder.toString === "ScalaTest is clear!")
        assert(buffer === List("ScalaTest", "is", "concise!"))
      }
    }
  }
}

Overriding `withFixture(NoArgTest)`

Although the get-fixture method and fixture-context object approaches take care of setting up a fixture at the beginning of each test, they don't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgTest), one of ScalaTest's lifecycle methods defined in trait Suite.

Trait Suite's implementation of runTest passes a no-arg test function to withFixture(NoArgTest). It is withFixture's responsibility to invoke that test function. Suite's implementation of withFixture simply invokes the function, like this:

// Default implementation in trait Suite
protected def withFixture(test: NoArgTest) = {
  test()
}

You can, therefore, override withFixture to perform setup before and/or cleanup after invoking the test function. If you have cleanup to perform, you should invoke the test function inside a try block and perform the cleanup in a finally clause, in case an exception propagates back through withFixture. (If a test fails because of an exception, the test function invoked by withFixture will result in a Failed wrapping the exception. Nevertheless, best practice is to perform cleanup in a finally clause just in case an exception occurs.)

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. In other words, instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgTest) = {
  // Perform setup
  try super.withFixture(test) // Invoke the test function
  finally {
    // Perform cleanup
  }
}

Here's an example in which withFixture(NoArgTest) is used to take a snapshot of the working directory if a test fails, and send that information to the reporter:

package org.scalatest.examples.funspec.noargtest

import java.io.File
import org.scalatest._

class ExampleSpec extends FunSpec {

  override def withFixture(test: NoArgTest) = {

    try super.withFixture(test) match {
      case failed: Failed =>
        val currDir = new File(".")
        val fileNames = currDir.list()
        info("Dir snapshot: " + fileNames.mkString(", "))
        failed
      case other => other
    }
  }

  describe("This test") {
    it("should succeed") {
      assert(1 + 1 === 2)
    }

    it("should fail") {
      assert(1 + 1 === 3)
    }
  }
}

Running this version of ExampleSuite in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSuite)
ExampleSuite:
This test
- should succeed
- should fail *** FAILED ***
  2 did not equal 3 (:33)
  + Dir snapshot: hello.txt, world.txt

Note that the NoArgTest passed to withFixture, in addition to an apply method that executes the test, also includes the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

package org.scalatest.examples.funspec.loanfixture

import java.util.concurrent.ConcurrentHashMap

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer
    databases.put(name, db)
    db
  }
  def removeDb(name: String) {
    databases.remove(name)
  }
}

import org.scalatest.FunSpec
import DbServer._
import java.util.UUID.randomUUID
import java.io._

class ExampleSpec extends FunSpec {

  def withDatabase(testCode: Db => Any) {
    val dbName = randomUUID.toString
    val db = createDb(dbName) // create the fixture
    try {
      db.append("ScalaTest is ") // perform setup
      testCode(db) // "loan" the fixture to the test
    }
    finally removeDb(dbName) // clean up the fixture
  }

  def withFile(testCode: (File, FileWriter) => Any) {
    val file = File.createTempFile("hello", "world") // create the fixture
    val writer = new FileWriter(file)
    try {
      writer.write("ScalaTest is ") // set up the fixture
      testCode(file, writer) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  describe("Testing") {
    // This test needs the file fixture
    it("should be productive") {
      withFile { (file, writer) =>
        writer.write("productive!")
        writer.flush()
        assert(file.length === 24)
      }
    }
  }

  describe("Test code") {
    // This test needs the database fixture
    it("should be readable") {
      withDatabase { db =>
        db.append("readable!")
        assert(db.toString === "ScalaTest is readable!")
      }
    }

    // This test needs both the file and the database
    it("should be clear and concise") {
      withDatabase { db =>
       withFile { (file, writer) => // loan-fixture methods compose
          db.append("clear!")
          writer.write("concise!")
          writer.flush()
          assert(db.toString === "ScalaTest is clear!")
          assert(file.length === 21)
        }
      }
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating files or databases, it is a good idea to give each file or database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.Suite and overriding withFixture(OneArgTest). Each test in a fixture.Suite takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgTest. This withFixture method is responsible for invoking the one-arg test function, so you can perform fixture set up before, and clean up after, invoking and passing the fixture into the test function.

To enable the stacking of traits that define withFixture(NoArgTest), it is a good idea to let withFixture(NoArgTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgTest to a NoArgTest. You can do that by passing the fixture object to the toNoArgTest method of OneArgTest. In other words, instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgTest) method of the same instance by writing:

withFixture(test.toNoArgTest(theFixture))

Here's a complete example:

package org.scalatest.examples.funspec.oneargtest

import org.scalatest.fixture
import java.io._

class ExampleSpec extends fixture.FunSpec {

  case class FixtureParam(file: File, writer: FileWriter)

  def withFixture(test: OneArgTest) = {

    // create the fixture
    val file = File.createTempFile("hello", "world")
    val writer = new FileWriter(file)
    val theFixture = FixtureParam(file, writer)

    try {
      writer.write("ScalaTest is ") // set up the fixture
      withFixture(test.toNoArgTest(theFixture)) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  describe("Testing") {
    it("should be easy") { f =>
      f.writer.write("easy!")
      f.writer.flush()
      assert(f.file.length === 18)
    }

    it("should be fun") { f =>
      f.writer.write("fun!")
      f.writer.flush()
      assert(f.file.length === 17)
    }
  }
}

In this example, the tests actually required two fixture objects, a File and a FileWriter. In such situations you can simply define the FixtureParam type to be a tuple containing the objects, or as is done in this example, a case class containing the objects. For more information on the withFixture(OneArgTest) technique, see the documentation for fixture.FunSpec.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.funspec.beforeandafter

import org.scalatest.FunSpec
import org.scalatest.BeforeAndAfter
import collection.mutable.ListBuffer

class ExampleSpec extends FunSpec with BeforeAndAfter {

  val builder = new StringBuilder
  val buffer = new ListBuffer[String]

  before {
    builder.append("ScalaTest is ")
  }

  after {
    builder.clear()
    buffer.clear()
  }

  describe("Testing") {
    it("should be easy") {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    it("should be fun") {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
    }
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state. This is why ScalaTest's ParallelTestExecution trait extends OneInstancePerTest. By running each test in its own instance of the class, each test has its own copy of the instance variables, so you don't need to synchronize. If you mixed ParallelTestExecution into the ExampleSuite above, the tests would run in parallel just fine without any synchronization needed on the mutable StringBuilder and ListBuffer[String] objects.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilder and ListBuffer[String] fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.funspec.composingwithfixture

import org.scalatest._
import collection.mutable.ListBuffer

trait Builder extends TestSuiteMixin { this: TestSuite =>

  val builder = new StringBuilder

  abstract override def withFixture(test: NoArgTest) = {
    builder.append("ScalaTest is ")
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally builder.clear()
  }
}

trait Buffer extends TestSuiteMixin { this: TestSuite =>

  val buffer = new ListBuffer[String]

  abstract override def withFixture(test: NoArgTest) = {
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally buffer.clear()
  }
}

class ExampleSpec extends FunSpec with Builder with Buffer {

  describe("Testing") {
    it("should be easy") {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    it("should be fun") {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }
  }
}

By mixing in both the Builder and Buffer traits, ExampleSuite gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Spec extends FunSpec with Buffer with Builder

And if you only need one fixture you mix in only that trait:

class Example3Spec extends FunSpec with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.funspec.composingbeforeandaftereach

import org.scalatest._
import org.scalatest.BeforeAndAfterEach
import collection.mutable.ListBuffer

trait Builder extends BeforeAndAfterEach { this: Suite =>

  val builder = new StringBuilder

  override def beforeEach() {
    builder.append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builder.clear()
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  val buffer = new ListBuffer[String]

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally buffer.clear()
  }
}

class ExampleSpec extends FunSpec with Builder with Buffer {

  describe("Testing") {
    it("should be easy") {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    it("should be fun") {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in a FunSpec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any FunSpec that uses them, so that the tests they contain will be registered as tests in that FunSpec. For example, given this stack class:

import scala.collection.mutable.ListBuffer

class Stack[T] {

  val MAX = 10
  private val buf = new ListBuffer[T]

  def push(o: T) {
    if (!full)
      buf.prepend(o)
    else
      throw new IllegalStateException("can't push onto a full stack")
  }

  def pop(): T = {
    if (!empty)
      buf.remove(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def peek: T = {
    if (!empty)
      buf(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def full: Boolean = buf.size == MAX
  def empty: Boolean = buf.size == 0
  def size = buf.size

  override def toString = buf.mkString("Stack(", ", ", ")")
}

You may want to test the Stack class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several tests that make sense any time the stack is non-empty. Thus you'd ideally want to run those same tests for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these tests out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your FunSpec for stack, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared tests are run for all three fixtures. You can define a behavior function that encapsulates these shared tests inside the FunSpec that uses them. If they are shared between different FunSpecs, however, you could also define them in a separate trait that is mixed into each FunSpec that uses them.

For example, here the nonEmptyStack behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared tests for non-full stacks:

trait StackBehaviors { this: FunSpec =>

  def nonEmptyStack(newStack: => Stack[Int], lastItemAdded: Int) {

    it("should be non-empty") {
      assert(!newStack.empty)
    }

    it("should return the top item on peek") {
      assert(newStack.peek === lastItemAdded)
    }

    it("should not remove the top item on peek") {
      val stack = newStack
      val size = stack.size
      assert(stack.peek === lastItemAdded)
      assert(stack.size === size)
    }

    it("should remove the top item on pop") {
      val stack = newStack
      val size = stack.size
      assert(stack.pop === lastItemAdded)
      assert(stack.size === size - 1)
    }
  }

  def nonFullStack(newStack: => Stack[Int]) {

    it("should not be full") {
      assert(!newStack.full)
    }

    it("should add to the top on push") {
      val stack = newStack
      val size = stack.size
      stack.push(7)
      assert(stack.size === size + 1)
      assert(stack.peek === 7)
    }
  }
}

Given these behavior functions, you could invoke them directly, but FunSpec offers a DSL for the purpose, which looks like this:

it should behave like nonEmptyStack(stackWithOneItem, lastValuePushed)
it should behave like nonFullStack(stackWithOneItem)

If you prefer to use an imperative style to change fixtures, for example by mixing in BeforeAndAfterEach and reassigning a stack var in beforeEach, you could write your behavior functions in the context of that var, which means you wouldn't need to pass in the stack fixture because it would be in scope already inside the behavior function. In that case, your code would look like this:

it should behave like nonEmptyStack // assuming lastValuePushed is also in scope inside nonEmptyStack
it should behave like nonFullStack

The recommended style, however, is the functional, pass-all-the-needed-values-in style. Here's an example:

class SharedTestExampleSpec extends FunSpec with StackBehaviors {

  // Stack fixture creation methods
  def emptyStack = new Stack[Int]

  def fullStack = {
    val stack = new Stack[Int]
    for (i <- 0 until stack.MAX)
      stack.push(i)
    stack
  }

  def stackWithOneItem = {
    val stack = new Stack[Int]
    stack.push(9)
    stack
  }

  def stackWithOneItemLessThanCapacity = {
    val stack = new Stack[Int]
    for (i <- 1 to 9)
      stack.push(i)
    stack
  }

  val lastValuePushed = 9

  describe("A Stack") {

    describe("(when empty)") {

      it("should be empty") {
        assert(emptyStack.empty)
      }

      it("should complain on peek") {
        assertThrows[IllegalStateException] {
          emptyStack.peek
        }
      }

      it("should complain on pop") {
        assertThrows[IllegalStateException] {
          emptyStack.pop
        }
      }
    }

    describe("(with one item)") {
      it should behave like nonEmptyStack(stackWithOneItem, lastValuePushed)
      it should behave like nonFullStack(stackWithOneItem)
    }

    describe("(with one item less than capacity)") {
      it should behave like nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed)
      it should behave like nonFullStack(stackWithOneItemLessThanCapacity)
    }

    describe("(full)") {

      it("should be full") {
        assert(fullStack.full)
      }

      it should behave like nonEmptyStack(fullStack, lastValuePushed)

      it("should complain on a push") {
        assertThrows[IllegalStateException] {
          fullStack.push(10)
        }
      }
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> org.scalatest.run(new StackSpec)
A Stack (when empty)
- should be empty
- should complain on peek
- should complain on pop
A Stack (with one item)
- should be non-empty
- should return the top item on peek
- should not remove the top item on peek
- should remove the top item on pop
- should not be full
- should add to the top on push
A Stack (with one item less than capacity)
- should be non-empty
- should return the top item on peek
- should not remove the top item on peek
- should remove the top item on pop
- should not be full
- should add to the top on push
A Stack (full)
- should be full
- should be non-empty
- should return the top item on peek
- should not remove the top item on peek
- should remove the top item on pop
- should complain on a push

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. A good way to solve this problem in a FunSpec is to surround each invocation of a behavior function with a describe clause, which will prepend a string to each test name. For example, the following code in a FunSpec would register a test with the name "A Stack (when empty) should be empty":

describe("A Stack") {

  describe("(when empty)") {

    it("should be empty") {
      assert(emptyStack.empty)
    }
    // ...

If the "should be empty" test was factored out into a behavior function, it could be called repeatedly so long as each invocation of the behavior function is inside a different set of describe clauses.

trait FunSpecLike extends TestSuite with TestRegistration with Informing with Notifying with Alerting with Documenting

Implementation trait for class FunSpec, which facilitates a “behavior-driven” style of development (BDD), in which tests are combined with text that specifies the behavior the tests verify.

FunSpec is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of FunSpec into some other class, you can use this trait instead, because class FunSpec does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of FunSpec.

class FunSuite extends FunSuiteLike

A suite of tests in which each test is represented as a function value.

A suite of tests in which each test is represented as a function value. The “Fun” in FunSuite stands for “function.”

Recommended Usage: For teams coming from xUnit, FunSuite feels comfortable and familiar while still giving some benefits of BDD: FunSuite makes it easy to write descriptive test names, natural to write focused tests, and generates specification-like output that can facilitate communication among stakeholders.

Here's an example FunSuite:

package org.scalatest.examples.funsuite

import org.scalatest.FunSuite

class SetSuite extends FunSuite {

  test("An empty Set should have size 0") {
    assert(Set.empty.size === 0)
  }

  test("Invoking head on an empty Set should produce NoSuchElementException") {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

“test” is a method, defined in FunSuite, which will be invoked by the primary constructor of SetSuite. You specify the name of the test as a string between the parentheses, and the test code itself between curly braces. The test code is a function passed as a by-name parameter to test, which registers it for later execution.

A FunSuite's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Tests can only be registered with the test method while the FunSuite is in its registration phase. Any attempt to register a test after the FunSuite has entered its ready phase, i.e., after run has been invoked on the FunSuite, will be met with a thrown TestRegistrationClosedException. The recommended style of using FunSuite is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Note: FunSuite was in part inspired by Rehersal, an early test framework for Scala.

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, FunSuite provides registration methods that start with ignore instead of test. Here's an example:

package org.scalatest.examples.funsuite.ignore

import org.scalatest.FunSuite

class SetSuite extends FunSuite {

  ignore("An empty Set should have size 0") {
    assert(Set.empty.size === 0)
  }

  test("Invoking head on an empty Set should produce NoSuchElementException") {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

If you run this version of SetSuite with:

scala> org.scalatest.run(new SetSuite)

It will run only the second test and report that the first test was ignored:

SetSuite:
- An empty Set should have size 0 !!! IGNORED !!!
- Invoking head on an empty Set should produce NoSuchElementException

If you wish to temporarily ignore an entire suite of tests, you can (on the JVM, not Scala.js) annotate the test class with @Ignore, like this:

package org.scalatest.examples.funsuite.ignoreall

import org.scalatest.FunSuite
import org.scalatest.Ignore

@Ignore
class SetSuite extends FunSuite {

  test("An empty Set should have size 0") {
    assert(Set.empty.size === 0)
  }

  test("Invoking head on an empty Set should produce NoSuchElementException") {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the SetSuite in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above SetSuite in the Scala interpreter, you'll see:

scala> org.scalatest.run(new SetSuite)
SetSuite:
- An empty Set should have size 0 !!! IGNORED !!!
- Invoking head on an empty Set should produce NoSuchElementException !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class visible, to encourage the developers to eventually fix and “un-ignore” it. If you want to prevent a class from being discovered at all (on the JVM, not Scala.js), use the DoNotDiscover annotation instead.

Informers

One of the parameters to FunSuite's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the reporting done by default by FunSuite's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event. Here's an example that shows both a direct use as well as an indirect use through the methods of GivenWhenThen:

package org.scalatest.examples.funsuite.info

import collection.mutable
import org.scalatest._

class SetSuite extends FunSuite with GivenWhenThen {

  test("An element can be added to an empty mutable Set") {

    Given("an empty mutable Set")
    val set = mutable.Set.empty[String]

    When("an element is added")
    set += "clarity"

    Then("the Set should have size 1")
    assert(set.size === 1)

    And("the Set should contain the added element")
    assert(set.contains("clarity"))

    info("That's all folks!")
  }
}

If you run this FunSuite from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSuite)
SetSuite:
- an element can be added to an empty mutable Set
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

Documenters

FunSuite also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example FunSuite that uses markup:

package org.scalatest.examples.funsuite.markup

import collection.mutable
import org.scalatest._

class SetSuite extends FunSuite with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

    def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  test("An element can be added to an empty mutable Set") {

    Given("an empty mutable Set")
    val set = mutable.Set.empty[String]

    When("an element is added")
    set += "clarity"

    Then("the Set should have size 1")
    assert(set.size === 1)

    And("the Set should contain the added element")
    assert(set.contains("clarity"))

    markup("This test finished with a **bold** statement!")
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.funsuite.note

import collection.mutable
import org.scalatest._

class SetSuite extends FunSuite {

  test("An element can be added to an empty mutable Set") {

    info("info is recorded")
    markup("markup is *also* recorded")
    note("notes are sent immediately")
    alert("alerts are also sent immediately")

    val set = mutable.Set.empty[String]
    set += "clarity"
    assert(set.size === 1)
    assert(set.contains("clarity"))
  }
}

Because note and alert information is sent immediately, it will appear before the test name in string reporters, and its color will be unrelated to the ultimate outcome of the test: note text will always appear in green, alert text will always appear in yellow. Here's an example:

scala> org.scalatest.run(new SetSpec)
SetSuite:
  + notes are sent immediately
  + alerts are also sent immediately
- An element can be added to an empty mutable Set
  + info is recorded
  + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. The test can also include some code that sends more information about the behavior to the reporter when the tests run. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality, has not yet been implemented.

Although pending tests may be used more often in specification-style suites, such as org.scalatest.FunSpec, you can also use it in FunSuite, like this:

package org.scalatest.examples.funsuite.pending

import org.scalatest._

class SetSuite extends FunSuite {

  test("An empty Set should have size 0") (pending)

  test("Invoking head on an empty Set should produce NoSuchElementException") {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

(Note: "(pending)" is the body of the test. Thus the test contains just one statement, an invocation of the pending method, which throws TestPendingException.) If you run this version of SetSuite with:

scala> org.scalatest.run(new SetSuite)

It will run both tests, but report that first test is pending. You'll see:

SetSuite:
- An empty Set should have size 0 (pending)
- Invoking head on an empty Set should produce NoSuchElementException

One difference between an ignored test and a pending one is that an ignored test is intended to be used during a significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException. The reason for this difference is that it enables your unfinished test to send InfoProvided messages to the reporter before it completes abruptly with TestPendingException, as shown in the previous example on Informers that used the GivenWhenThen trait.

Tagging tests

A FunSuite's tests may be classified into groups by tagging them with string names. As with any suite, when executing a FunSuite, groups of tests can optionally be included and/or excluded. To tag a FunSuite's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for FunSuites like this:

package org.scalatest.examples.funsuite.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place FunSuite tests into groups with tags like this:

import org.scalatest.FunSuite
import org.scalatest.tagobjects.Slow

class SetSuite extends FunSuite {

  test("An empty Set should have size 0", Slow) {
    assert(Set.empty.size === 0)
  }

  test("Invoking head on an empty Set should produce NoSuchElementException",
       Slow, DbTest) {
    assertThrows[NoSuchElementException] {
      Set.empty.head
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of a FunSuite in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and more amenable for parallel test execution.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
fixture-context objects	By placing fixture methods and fields into traits, you can easily give each test just the newly created fixtures it needs by mixing together traits. Use this technique when you need different combinations of mutable fixture objects in different tests, and don't need to clean up after.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgTest)` instead)
`withFixture(OneArgTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or an holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.funsuite.getfixture

import org.scalatest.FunSuite
import collection.mutable.ListBuffer

class ExampleSuite extends FunSuite {

  class Fixture {
    val builder = new StringBuilder("ScalaTest is ")
    val buffer = new ListBuffer[String]
  }

  def fixture = new Fixture

  test("Testing should be easy") {
    val f = fixture
    f.builder.append("easy!")
    assert(f.builder.toString === "ScalaTest is easy!")
    assert(f.buffer.isEmpty)
    f.buffer += "sweet"
  }

  test("Testing should be fun") {
    val f = fixture
    f.builder.append("fun!")
    assert(f.builder.toString === "ScalaTest is fun!")
    assert(f.buffer.isEmpty)
  }
}

The “f.” in front of each use of a fixture object provides a visual indication of which objects are part of the fixture, but if you prefer, you can import the the members with “import f._” and use the names directly.

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, if you could pass in an initial value for a mutable fixture object as a parameter to the get-fixture method.

Instantiating fixture-context objects

An alternate technique that is especially useful when different tests need different combinations of fixture objects is to define the fixture objects as instance variables of fixture-context objects whose instantiation forms the body of tests. Like get-fixture methods, fixture-context objects are only appropriate if you don't need to clean up the fixtures after using them.

To use this technique, you define instance variables intialized with fixture objects in traits and/or classes, then in each test instantiate an object that contains just the fixture objects needed by the test. Traits allow you to mix together just the fixture objects needed by each test, whereas classes allow you to pass data in via a constructor to configure the fixture objects. Here's an example in which fixture objects are partitioned into two traits and each test just mixes together the traits it needs:

package org.scalatest.examples.funsuite.fixturecontext

import collection.mutable.ListBuffer
import org.scalatest.FunSuite

class ExampleSuite extends FunSuite {

  trait Builder {
    val builder = new StringBuilder("ScalaTest is ")
  }

  trait Buffer {
    val buffer = ListBuffer("ScalaTest", "is")
  }

  // This test needs the StringBuilder fixture
  test("Testing should be productive") {
    new Builder {
      builder.append("productive!")
      assert(builder.toString === "ScalaTest is productive!")
    }
  }

  // This test needs the ListBuffer[String] fixture
  test("Test code should be readable") {
    new Buffer {
      buffer += ("readable!")
      assert(buffer === List("ScalaTest", "is", "readable!"))
    }
  }

  // This test needs both the StringBuilder and ListBuffer
  test("Test code should be clear and concise") {
    new Builder with Buffer {
      builder.append("clear!")
      buffer += ("concise!")
      assert(builder.toString === "ScalaTest is clear!")
      assert(buffer === List("ScalaTest", "is", "concise!"))
    }
  }
}

Overriding `withFixture(NoArgTest)`

Although the get-fixture method and fixture-context object approaches take care of setting up a fixture at the beginning of each test, they don't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgTest), one of ScalaTest's lifecycle methods defined in trait Suite.

Trait Suite's implementation of runTest passes a no-arg test function to withFixture(NoArgTest). It is withFixture's responsibility to invoke that test function. Suite's implementation of withFixture simply invokes the function, like this:

// Default implementation in trait Suite
protected def withFixture(test: NoArgTest) = {
  test()
}

You can, therefore, override withFixture to perform setup before and/or cleanup after invoking the test function. If you have cleanup to perform, you should invoke the test function inside a try block and perform the cleanup in a finally clause, in case an exception propagates back through withFixture. (If a test fails because of an exception, the test function invoked by withFixture will result in a Failed wrapping the exception. Nevertheless, best practice is to perform cleanup in a finally clause just in case an exception occurs.)

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. In other words, instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgTest) = {
  // Perform setup
  try super.withFixture(test) // Invoke the test function
  finally {
    // Perform cleanup
  }
}

Here's an example in which withFixture(NoArgTest) is used to take a snapshot of the working directory if a test fails, and send that information to the reporter:

package org.scalatest.examples.funsuite.noargtest

import java.io.File
import org.scalatest._

class ExampleSuite extends FunSuite {

  override def withFixture(test: NoArgTest) = {

    super.withFixture(test) match {
      case failed: Failed =>
        val currDir = new File(".")
        val fileNames = currDir.list()
        info("Dir snapshot: " + fileNames.mkString(", "))
        failed
      case other => other
    }
  }

  test("This test should succeed") {
    assert(1 + 1 === 2)
  }

  test("This test should fail") {
    assert(1 + 1 === 3)
  }
}

Running this version of ExampleSuite in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSuite)
ExampleSuite:
- this test should succeed
- this test should fail *** FAILED ***
  2 did not equal 3 (:33)
  + Dir snapshot: hello.txt, world.txt

Note that the NoArgTest passed to withFixture, in addition to an apply method that executes the test, also includes the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

package org.scalatest.examples.funsuite.loanfixture

import java.util.concurrent.ConcurrentHashMap

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer
    databases.put(name, db)
    db
  }
  def removeDb(name: String) {
    databases.remove(name)
  }
}

import org.scalatest.FunSuite
import DbServer._
import java.util.UUID.randomUUID
import java.io._

class ExampleSuite extends FunSuite {

  def withDatabase(testCode: Db => Any) {
    val dbName = randomUUID.toString
    val db = createDb(dbName) // create the fixture
    try {
      db.append("ScalaTest is ") // perform setup
      testCode(db) // "loan" the fixture to the test
    }
    finally removeDb(dbName) // clean up the fixture
  }

  def withFile(testCode: (File, FileWriter) => Any) {
    val file = File.createTempFile("hello", "world") // create the fixture
    val writer = new FileWriter(file)
    try {
      writer.write("ScalaTest is ") // set up the fixture
      testCode(file, writer) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  // This test needs the file fixture
  test("Testing should be productive") {
    withFile { (file, writer) =>
      writer.write("productive!")
      writer.flush()
      assert(file.length === 24)
    }
  }

  // This test needs the database fixture
  test("Test code should be readable") {
    withDatabase { db =>
      db.append("readable!")
      assert(db.toString === "ScalaTest is readable!")
    }
  }

  // This test needs both the file and the database
  test("Test code should be clear and concise") {
    withDatabase { db =>
      withFile { (file, writer) => // loan-fixture methods compose
        db.append("clear!")
        writer.write("concise!")
        writer.flush()
        assert(db.toString === "ScalaTest is clear!")
        assert(file.length === 21)
      }
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating files or databases, it is a good idea to give each file or database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.Suite and overriding withFixture(OneArgTest). Each test in a fixture.Suite takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgTest. This withFixture method is responsible for invoking the one-arg test function, so you can perform fixture set up before, and clean up after, invoking and passing the fixture into the test function.

To enable the stacking of traits that define withFixture(NoArgTest), it is a good idea to let withFixture(NoArgTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgTest to a NoArgTest. You can do that by passing the fixture object to the toNoArgTest method of OneArgTest. In other words, instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgTest) method of the same instance by writing:

withFixture(test.toNoArgTest(theFixture))

Here's a complete example:

package org.scalatest.examples.funsuite.oneargtest

import org.scalatest.fixture
import java.io._

class ExampleSuite extends fixture.FunSuite {

  case class FixtureParam(file: File, writer: FileWriter)

  def withFixture(test: OneArgTest) = {

    // create the fixture
    val file = File.createTempFile("hello", "world")
    val writer = new FileWriter(file)
    val theFixture = FixtureParam(file, writer)

    try {
      writer.write("ScalaTest is ") // set up the fixture
      withFixture(test.toNoArgTest(theFixture)) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  test("Testing should be easy") { f =>
    f.writer.write("easy!")
    f.writer.flush()
    assert(f.file.length === 18)
  }

  test("Testing should be fun") { f =>
    f.writer.write("fun!")
    f.writer.flush()
    assert(f.file.length === 17)
  }
}

In this example, the tests actually required two fixture objects, a File and a FileWriter. In such situations you can simply define the FixtureParam type to be a tuple containing the objects, or as is done in this example, a case class containing the objects. For more information on the withFixture(OneArgTest) technique, see the documentation for fixture.FunSuite.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.funsuite.beforeandafter

import org.scalatest.FunSuite
import org.scalatest.BeforeAndAfter
import collection.mutable.ListBuffer

class ExampleSuite extends FunSuite with BeforeAndAfter {

  val builder = new StringBuilder
  val buffer = new ListBuffer[String]

  before {
    builder.append("ScalaTest is ")
  }

  after {
    builder.clear()
    buffer.clear()
  }

  test("testing should be easy") {
    builder.append("easy!")
    assert(builder.toString === "ScalaTest is easy!")
    assert(buffer.isEmpty)
    buffer += "sweet"
  }

  test("testing should be fun") {
    builder.append("fun!")
    assert(builder.toString === "ScalaTest is fun!")
    assert(buffer.isEmpty)
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state. This is why ScalaTest's ParallelTestExecution trait extends OneInstancePerTest. By running each test in its own instance of the class, each test has its own copy of the instance variables, so you don't need to synchronize. If you mixed ParallelTestExecution into the ExampleSuite above, the tests would run in parallel just fine without any synchronization needed on the mutable StringBuilder and ListBuffer[String] objects.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilder and ListBuffer[String] fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.funsuite.composingwithfixture

import org.scalatest._
import collection.mutable.ListBuffer

trait Builder extends TestSuiteMixin { this: TestSuite =>

  val builder = new StringBuilder

  abstract override def withFixture(test: NoArgTest) = {
    builder.append("ScalaTest is ")
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally builder.clear()
  }
}

trait Buffer extends TestSuiteMixin { this: TestSuite =>

  val buffer = new ListBuffer[String]

  abstract override def withFixture(test: NoArgTest) = {
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally buffer.clear()
  }
}

class ExampleSuite extends FunSuite with Builder with Buffer {

  test("Testing should be easy") {
    builder.append("easy!")
    assert(builder.toString === "ScalaTest is easy!")
    assert(buffer.isEmpty)
    buffer += "sweet"
  }

  test("Testing should be fun") {
    builder.append("fun!")
    assert(builder.toString === "ScalaTest is fun!")
    assert(buffer.isEmpty)
    buffer += "clear"
  }
}

By mixing in both the Builder and Buffer traits, ExampleSuite gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Suite extends FunSuite with Buffer with Builder

And if you only need one fixture you mix in only that trait:

class Example3Suite extends FunSuite with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.funsuite.composingbeforeandaftereach

import org.scalatest._
import org.scalatest.BeforeAndAfterEach
import collection.mutable.ListBuffer

trait Builder extends BeforeAndAfterEach { this: Suite =>

  val builder = new StringBuilder

  override def beforeEach() {
    builder.append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try {
      super.afterEach() // To be stackable, must call super.afterEach
    }
    finally builder.clear()
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  val buffer = new ListBuffer[String]

  override def afterEach() {
    try {
      super.afterEach() // To be stackable, must call super.afterEach
    }
    finally buffer.clear()
  }
}

class ExampleSuite extends FunSuite with Builder with Buffer {

  test("Testing should be easy") {
    builder.append("easy!")
    assert(builder.toString === "ScalaTest is easy!")
    assert(buffer.isEmpty)
    buffer += "sweet"
  }

  test("Testing should be fun") {
    builder.append("fun!")
    assert(builder.toString === "ScalaTest is fun!")
    assert(buffer.isEmpty)
    buffer += "clear"
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in a FunSuite, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any FunSuite that uses them, so that the tests they contain will be registered as tests in that FunSuite. For example, given this stack class:

import scala.collection.mutable.ListBuffer

class Stack[T] {

  val MAX = 10
  private val buf = new ListBuffer[T]

  def push(o: T) {
    if (!full)
      buf.prepend(o)
    else
      throw new IllegalStateException("can't push onto a full stack")
  }

  def pop(): T = {
    if (!empty)
      buf.remove(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def peek: T = {
    if (!empty)
      buf(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def full: Boolean = buf.size == MAX
  def empty: Boolean = buf.size == 0
  def size = buf.size

  override def toString = buf.mkString("Stack(", ", ", ")")
}

You may want to test the Stack class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several tests that make sense any time the stack is non-empty. Thus you'd ideally want to run those same tests for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these tests out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your FunSuite for stack, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared tests are run for all three fixtures.

You can define a behavior function that encapsulates these shared tests inside the FunSuite that uses them. If they are shared between different FunSuites, however, you could also define them in a separate trait that is mixed into each FunSuite that uses them. For example, here the nonEmptyStack behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared tests for non-full stacks:

import org.scalatest.FunSuite

trait FunSuiteStackBehaviors { this: FunSuite =>

  def nonEmptyStack(createNonEmptyStack: => Stack[Int], lastItemAdded: Int) {

    test("empty is invoked on this non-empty stack: " + createNonEmptyStack.toString) {
      val stack = createNonEmptyStack
      assert(!stack.empty)
    }

    test("peek is invoked on this non-empty stack: " + createNonEmptyStack.toString) {
      val stack = createNonEmptyStack
      val size = stack.size
      assert(stack.peek === lastItemAdded)
      assert(stack.size === size)
    }

    test("pop is invoked on this non-empty stack: " + createNonEmptyStack.toString) {
      val stack = createNonEmptyStack
      val size = stack.size
      assert(stack.pop === lastItemAdded)
      assert(stack.size === size - 1)
    }
  }

  def nonFullStack(createNonFullStack: => Stack[Int]) {

    test("full is invoked on this non-full stack: " + createNonFullStack.toString) {
      val stack = createNonFullStack
      assert(!stack.full)
    }

    test("push is invoked on this non-full stack: " + createNonFullStack.toString) {
      val stack = createNonFullStack
      val size = stack.size
      stack.push(7)
      assert(stack.size === size + 1)
      assert(stack.peek === 7)
    }
  }
}

Given these behavior functions, you could invoke them directly, but FunSuite offers a DSL for the purpose, which looks like this:

testsFor(nonEmptyStack(stackWithOneItem, lastValuePushed))
testsFor(nonFullStack(stackWithOneItem))

If you prefer to use an imperative style to change fixtures, for example by mixing in BeforeAndAfterEach and reassigning a stack var in beforeEach, you could write your behavior functions in the context of that var, which means you wouldn't need to pass in the stack fixture because it would be in scope already inside the behavior function. In that case, your code would look like this:

testsFor(nonEmptyStack) // assuming lastValuePushed is also in scope inside nonEmptyStack
testsFor(nonFullStack)

The recommended style, however, is the functional, pass-all-the-needed-values-in style. Here's an example:

import org.scalatest.FunSuite

class StackFunSuite extends FunSuite with FunSuiteStackBehaviors {

  // Stack fixture creation methods
  def emptyStack = new Stack[Int]

  def fullStack = {
    val stack = new Stack[Int]
    for (i <- 0 until stack.MAX)
      stack.push(i)
    stack
  }

  def stackWithOneItem = {
    val stack = new Stack[Int]
    stack.push(9)
    stack
  }

  def stackWithOneItemLessThanCapacity = {
    val stack = new Stack[Int]
    for (i <- 1 to 9)
      stack.push(i)
    stack
  }

  val lastValuePushed = 9

  test("empty is invoked on an empty stack") {
    val stack = emptyStack
    assert(stack.empty)
  }

  test("peek is invoked on an empty stack") {
    val stack = emptyStack
    assertThrows[IllegalStateException] {
      stack.peek
    }
  }

  test("pop is invoked on an empty stack") {
    val stack = emptyStack
    assertThrows[IllegalStateException] {
      stack.pop
    }
  }

  testsFor(nonEmptyStack(stackWithOneItem, lastValuePushed))
  testsFor(nonFullStack(stackWithOneItem))

  testsFor(nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed))
  testsFor(nonFullStack(stackWithOneItemLessThanCapacity))

  test("full is invoked on a full stack") {
    val stack = fullStack
    assert(stack.full)
  }

  testsFor(nonEmptyStack(fullStack, lastValuePushed))

  test("push is invoked on a full stack") {
    val stack = fullStack
    assertThrows[IllegalStateException] {
      stack.push(10)
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> org.scalatest.run(new StackFunSuite)
StackFunSuite:
- empty is invoked on an empty stack
- peek is invoked on an empty stack
- pop is invoked on an empty stack
- empty is invoked on this non-empty stack: Stack(9)
- peek is invoked on this non-empty stack: Stack(9)
- pop is invoked on this non-empty stack: Stack(9)
- full is invoked on this non-full stack: Stack(9)
- push is invoked on this non-full stack: Stack(9)
- empty is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
- peek is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
- pop is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
- full is invoked on this non-full stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
- push is invoked on this non-full stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
- full is invoked on a full stack
- empty is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
- peek is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
- pop is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
- push is invoked on a full stack

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. In a FunSuite there is no nesting construct analogous to FunSpec's describe clause. Therefore, you need to do a bit of extra work to ensure that the test names are unique. If a duplicate test name problem shows up in a FunSuite, you'll need to pass in a prefix or suffix string to add to each test name. You can pass this string the same way you pass any other data needed by the shared tests, or just call toString on the shared fixture object. This is the approach taken by the previous FunSuiteStackBehaviors example.

Given this FunSuiteStackBehaviors trait, calling it with the stackWithOneItem fixture, like this:

testsFor(nonEmptyStack(stackWithOneItem, lastValuePushed))

yields test names:

empty is invoked on this non-empty stack: Stack(9)
peek is invoked on this non-empty stack: Stack(9)
pop is invoked on this non-empty stack: Stack(9)

Whereas calling it with the stackWithOneItemLessThanCapacity fixture, like this:

testsFor(nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed))

yields different test names:

empty is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
peek is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
pop is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)

trait FunSuiteLike extends TestSuite with TestRegistration with Informing with Notifying with Alerting with Documenting

Implementation trait for class FunSuite, which represents a suite of tests in which each test is represented as a function value.

FunSuite is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of FunSuite into some other class, you can use this trait instead, because class FunSuite does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of FunSuite.

class FutureOutcome extends AnyRef

Wrapper class for Future[Outcome] that presents a more convenient API for manipulation in withFixture methods in async styles.

This type serves as the result type of both test functions and withFixture methods in ScalaTest's async styles. A Future[Outcome] is not used as this result type for two reasons. First, Outcome treats exceptions specially, and as a result methods on Future would usually not yield the desired Future[Outcome] result. Only run-aborting exceptions should result in a failed Future[Outcome]. Any other thrown exception other than TestCanceledException or TestPendingException should result in a successfulFuture containing a org.scalatest.Failed. A thrown TestCanceledException should result in a successful Future containing an org.scalatest.Canceled; A thrown TestPendingException should result in a successful Future containing a org.scalatest.Pending. If manipulating a Future[Outcome] directly, by contrast, any thrown exception would result in a failed Future.

Additionally, to be consistent with corresponding transformations in traditional testing styles, methods registering callbacks should return a new future outcome that doesn't complete until both the original future outcome has completed and the subsequent callback has completed execution. Additionally, if the callback itself throws an exception, that exception should determine the result of the future outcome returned by the callback registration method. This behavior is rather inconvenient to obtain on the current Future API, so FutureOutcome provides well-named methods that have this behavior.

Lastly, the FutureOutcome is intended to help prevent confusion by eliminating the need to work with types like scala.util.Success(org.scalatest.Failed). For this purpose a org.scalactic.Or is used instead of a scala.util.Try to describe results of FutureOutcome.

A FutureOutcome represents a computation that can result in an Outcome or an "abort." An abort means that a run-aborting exception occurred during the computation. Any other, non-run-aborting exception will be represented as an non-Succeeded Outcome: one of Failed, Canceled, or Pending.

The methods of FutureOutcome include the following callback registration methods:

onSucceededThen - registers a callback to be executed if the future outcome is Succeeded.
onFailedThen - registers a callback to be executed if the future outcome is Failed.
onCanceledThen - registers a callback to be executed if the future outcome is Canceled.
onPendingThen - registers a callback to be executed if the future outcome is Pending.
onOutcomeThen - registers a callback to be executed if the future outcome is actually an Outcome and not an abort.
onAbortedThen - registers a callback to be executed if the future outcome aborts.
onCompletedThen - registers a callback to be executed upon completion no matter how the future outcome completes.

The callback methods listed previously can be used to perform a side effect once a FutureOutcome completes. To change an Outcome into a different Outcome asynchronously, use the change registration method, which takes a function from Outcome to Outcome. The other methods on FutureOutcome, isCompleted and value, allow you to poll a FutureOutcome. None of the methods on FutureOutcome block. Lastly, because an implicit Futuristic instance is provided for FutureOutcome, you can use complete-lastly syntax with FutureOutcome.

trait GivenWhenThen extends AnyRef

Trait that contains methods named given, when, then, and and, which take a string message and implicit Informer, and forward the message to the informer.

Here's an example:

package org.scalatest.examples.flatspec.info

import collection.mutable
import org.scalatest._

class SetSpec extends FlatSpec with GivenWhenThen {

  "A mutable Set" should "allow an element to be added" in {
    Given("an empty mutable Set")
    val set = mutable.Set.empty[String]

    When("an element is added")
    set += "clarity"

    Then("the Set should have size 1")
    assert(set.size === 1)

    And("the Set should contain the added element")
    assert(set.contains("clarity"))

    info("That's all folks!")
  }
}

If you run this SetSpec from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSpec)
A mutable Set
- should allow an element to be added
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

trait Ignore extends Annotation

Annotation used to tag a test, or suite of tests, as ignored.

Note: This is actually an annotation defined in Java, not a Scala trait. It must be defined in Java instead of Scala so it will be accessible at runtime. It has been inserted into Scaladoc by pretending it is a trait.

If you wish to temporarily ignore an entire suite of tests, you can annotate the test class with @Ignore, like this:

package org.scalatest.examples.flatspec.ignoreall

import org.scalatest._

@Ignore
class SetSpec extends FlatSpec {

  "An empty Set" should "have size 0" in {
    assert(Set.empty.size === 0)
  }

  it should "produce NoSuchElementException when head is invoked" in {
    intercept[NoSuchElementException] {
      Set.empty.head
    }
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the SetSpec in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above SetSpec in the Scala interpreter, you'll see:

scala> org.scalatest.run(new SetSpec)
An empty Set
- should have size 0 !!! IGNORED !!!
- should produce NoSuchElementException when head is invoked !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class somewhat visible, to encourage the developers to eventually fix and un-ignore it. If you want to prevent a class from being discovered at all, use the DoNotDiscover annotation instead.

Another use case for @Ignore is to mark test methods as ignored in traits Spec and fixture.Spec. Here's an example:

package org.scalatest.examples.spec.ignore

import org.scalatest._

class SetSpec extends RefSpec {

  @Ignore def `an empty Set should have size 0` {
    assert(Set.empty.size === 0)
  }

  def `invoking head on an empty Set should produce NoSuchElementException` {
    intercept[NoSuchElementException] {
      Set.empty.head
    }
  }
}

If you run this version of SetSpec in the Scala interpreter, you'll see that it runs only the second test and reports that the first test was ignored:

scala> org.scalatest.run(new SetSpec)
SetSpec:
- an empty Set should have size 0 !!! IGNORED !!!
- invoking head on an empty Set should produce NoSuchElementException

Note that because reflection is not supported on Scala.js, this annotation will only work on the JVM, not on Scala.js.

trait Informer extends AnyRef

Trait to which custom information about a running suite of tests can be reported.

An Informer is essentially used to wrap a Reporter and provide easy ways to send custom information to that Reporter via an InfoProvided event. Informer contains an apply method that takes a string and an optional payload object of type Any. The Informer will forward the passed message string to the Reporter as the message parameter, and the optional payload object as the payload parameter, of an InfoProvided event.

Here's an example in which the Informer is used both directly via info method of trait FlatSpec and indirectly via the methods of trait GivenWhenThen:

package org.scalatest.examples.flatspec.info

import collection.mutable
import org.scalatest._

class SetSpec extends FlatSpec with GivenWhenThen {

  "A mutable Set" should "allow an element to be added" in {
    given("an empty mutable Set")
    val set = mutable.Set.empty[String]

    when("an element is added")
    set += "clarity"

    then("the Set should have size 1")
    assert(set.size === 1)

    and("the Set should contain the added element")
    assert(set.contains("clarity"))

    info("That's all folks!")
  }
}

If you run this SetSpec from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSpec)
A mutable Set
- should allow an element to be added
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

trait Informing extends AnyRef

Trait that contains the info method, which can be used to send info to the reporter.

trait Inside extends AnyRef

Trait containing the inside construct, which allows you to make statements about nested object graphs using pattern matching.

For example, given the following case classes:

case class Address(street: String, city: String, state: String, zip: String)
case class Name(first: String, middle: String, last: String)
case class Record(name: Name, address: Address, age: Int)

You could write:

inside (rec) { case Record(name, address, age) =>
  inside (name) { case Name(first, middle, last) =>
    first should be ("Sally")
    middle should be ("Ann")
    last should be ("Jones")
  }
  inside (address) { case Address(street, city, state, zip) =>
    street should startWith ("25")
    city should endWith ("Angeles")
    state should equal ("CA")
    zip should be ("12345")
  }
  age should be < 99
}

If an assertion fails, the error message will include the toString of each value passed to inside clauses enclosing the failed assertion. For example, if rec in the previous expression was defined like this:

val rec = Record(
  Name("Sally", "Anna", "Jones"),
  Address("25 Main St", "Los Angeles", "CA", "12345"),
  38
)

The error message will read:

"Ann[a]" was not equal to "Ann[]", inside Name(Sally,Anna,Jones),
inside Record(Name(Sally,Anna,Jones),Address(25 Main St,Los Angeles,CA,12345),38)

trait Inspectors extends AnyRef

Provides nestable inspector methods (or just inspectors) that enable assertions to be made about collections.

For example, the forAll method enables you to state that something should be true about all elements of a collection, such as that all elements should be positive:

scala> import org.scalatest._
import org.scalatest._

scala> import Assertions._
import Assertions._

scala> import Inspectors._
import Inspectors._

scala> val xs = List(1, 2, 3, 4, 5)
xs: List[Int] = List(1, 2, 3, 4, 5)

scala> forAll (xs) { x => assert(x > 0) }

Or, with matchers:

scala> import Matchers._
import Matchers._

scala> forAll (xs) { x => x should be > 0 }

To make assertions about nested collections, you can nest the inspector method invocations. For example, given the following list of lists of Int:

scala> val yss =
     |   List(
     |     List(1, 2, 3),
     |     List(1, 2, 3),
     |     List(1, 2, 3)
     |   )
yss: List[List[Int]] = List(List(1, 2, 3), List(1, 2, 3), List(1, 2, 3))

You can assert that all Int elements in all nested lists are positive by nesting two forAll method invocations, like this:

scala> forAll (yss) { ys =>
     |   forAll (ys) { y => y should be > 0 }
     | }

The full list of inspector methods are:

forAll - succeeds if the assertion holds true for every element
forAtLeast - succeeds if the assertion holds true for at least the specified number of elements
forAtMost - succeeds if the assertion holds true for at most the specified number of elements
forBetween - succeeds if the assertion holds true for between the specified minimum and maximum number of elements, inclusive
forEvery - same as forAll, but lists all failing elements if it fails (whereas forAll just reports the first failing element)
forExactly - succeeds if the assertion holds true for exactly the specified number of elements

The error messages produced by inspector methods are designed to make sense no matter how deeply you nest the method invocations. Here's an example of a nested inspection that fails and the resulting error message:

scala> forAll (yss) { ys =>
     |   forAll (ys) { y => y should be < 2 }
     | }
org.scalatest.exceptions.TestFailedException: forAll failed, because:
  at index 0, forAll failed, because:
    at index 1, 2 was not less than 2 (<console>:20)
  in List(1, 2, 3) (<console>:20)
in List(List(1, 2, 3), List(1, 2, 3), List(1, 2, 3))
     at org.scalatest.InspectorsHelper$.forAll(Inspectors.scala:146)
     ...

One way the error message is designed to help you understand the error is by using indentation that mimics the indentation of the source code (optimistically assuming the source will be nicely indented). The error message above indicates the outer forAll failed because its initial List (i.e., at index 0) failed the assertion, which was that all elements of that initial List[Int] at index 0 should be less than 2. This assertion failed because index 1 of that inner list contained the value 2, which was indeed “not less than 2.” The error message for the inner list is an indented line inside the error message for the outer list. The actual contents of each list are displayed at the end in inspector error messages, also indented appropriately. The actual contents are placed at the end so that for very large collections, the contents will not drown out and make it difficult to find the messages that describe actual causes of the failure.

The forAll and forEvery methods are similar in that both succeed only if the assertion holds for all elements of the collection. They differ in that forAll will only report the first element encountered that failed the assertion, but forEvery will report all elements that fail the assertion. The tradeoff is that while forEvery gives more information, it may take longer to run because it must inspect every element of the collection. The forAll method can simply stop inspecting once it encounters the first failing element. Here's an example that shows the difference in the forAll and forEvery error messages:

scala> forAll (xs) { x => x should be < 3 }
org.scalatest.exceptions.TestFailedException: forAll failed, because:
  at index 2, 3 was not less than 3 (<console>:18)
in List(1, 2, 3, 4, 5)
     at org.scalatest.InspectorsHelper$.forAll(Inspectors.scala:146)
     ...

scala> forEvery (xs) { x => x should be < 3 }
org.scalatest.exceptions.TestFailedException: forEvery failed, because:
  at index 2, 3 was not less than 3 (<console>:18),
  at index 3, 4 was not less than 3 (<console>:18),
  at index 4, 5 was not less than 3 (<console>:18)
in List(1, 2, 3, 4, 5)
     at org.scalatest.InspectorsHelper$.forEvery(Inspectors.scala:226)
     ...

Note that if you're using matchers, you can alternatively use inspector shorthands for writing non-nested inspections. Here's an example:

scala> all (xs) should be > 3
org.scalatest.exceptions.TestFailedException: 'all' inspection failed, because:
  at index 0, 1 was not greater than 3
in List(1, 2, 3, 4, 5)
     at org.scalatest.InspectorsHelper$.forAll(Inspectors.scala:146)

You can use Inspectors on any scala.collection.GenTraversable, java.util.Collection, java.util.Map (with Entry), Array, or String. Here are some examples:

scala> import org.scalatest._
import org.scalatest._

scala> import Inspectors._
import Inspectors._

scala> import Matchers._
import Matchers._

scala> forAll (Array(1, 2, 3)) { e => e should be < 5 }

scala> import collection.JavaConverters._
import collection.JavaConverters._

scala> val js = List(1, 2, 3).asJava
js: java.util.List[Int] = [1, 2, 3]

scala> forAll (js) { j => j should be < 5 }

scala> val jmap = Map("a" -> 1, "b" -> 2).asJava
jmap: java.util.Map[String,Int] = {a=1, b=2}

scala> forAtLeast(1, jmap) { e => e shouldBe Entry("b", 2) }

scala> forAtLeast(2, "hello, world!") { c => c shouldBe 'o' }

trait LoneElement extends AnyRef

Trait that provides an implicit conversion that adds to collection types a loneElement method, which will return the value of the lone element if the collection does indeed contain one and only one element, or throw TestFailedException if not.

This construct allows you to express in one statement that a collection should contain one and only one element and that the element value should meet some expectation. Here's an example:

set.loneElement should be > 9

Or, using an assertion instead of a matcher expression:

assert(set.loneElement > 9)

The loneElement syntax can be used with any collection type C for which an implicit Collecting[C] is available. ScalaTest provides implicit Collecting instances for scala.collection.GenTraversable, Array, and java.util.Collection. You can enable the loneElement syntax on other collection types by defining an implicit Collecting instances for those types.

If you want to use loneElement with a java.util.Map, first transform it to a set of entries with entrySet, and if helpful, use ScalaTest's Entry class:

scala> import org.scalatest._
import org.scalatest._

scala> import LoneElement._
import LoneElement._

scala> import Matchers._
import Matchers._

scala> val jmap = new java.util.HashMap[String, Int]
jmap: java.util.HashMap[String,Int] = {}

scala> jmap.put("one", 1)
res0: Int = 0

scala> jmap.entrySet.loneElement should be (Entry("one", 1))

trait Matchers extends Assertions with Tolerance with ShouldVerb with MatcherWords with Explicitly

Trait that provides a domain specific language (DSL) for expressing assertions in tests using the word should.

For example, if you mix Matchers into a suite class, you can write an equality assertion in that suite like this:

result should equal (3)

Here result is a variable, and can be of any type. If the object is an Int with the value 3, execution will continue (i.e., the expression will result in the unit value, ()). Otherwise, a TestFailedException will be thrown with a detail message that explains the problem, such as "7 did not equal 3". This TestFailedException will cause the test to fail.

Here is a table of contents for this documentation:

Matchers migration in ScalaTest 2.0
Checking equality with matchers
Checking size and length
Checking strings
Greater and less than
Checking Boolean properties with be
Using custom BeMatchers
Checking object identity
Checking an object's class
Checking numbers against a range
Checking for emptiness
Working with "containers"
Working with "aggregations"
Working with "sequences"
Working with "sortables"
Working with iterators
Inspector shorthands
Single-element collections
Java collections and maps
Strings and Arrays as collections
Be as an equality comparison
Being negative
Checking that a snippet of code does not compile
Logical expressions with and and or
Working with Options
Checking arbitrary properties with have
Using length and size with HavePropertyMatchers
Checking that an expression matches a pattern
Using custom matchers
Checking for expected exceptions
Those pesky parens

Trait MustMatchers is an alternative to Matchers that provides the exact same meaning, syntax, and behavior as Matchers, but uses the verb must instead of should. The two traits differ only in the English semantics of the verb: should is informal, making the code feel like conversation between the writer and the reader; must is more formal, making the code feel more like a written specification.

Checking equality with matchers

ScalaTest matchers provides five different ways to check equality, each designed to address a different need. They are:

result should equal (3) // can customize equality
result should === (3)   // can customize equality and enforce type constraints
result should be (3)    // cannot customize equality, so fastest to compile
result shouldEqual 3    // can customize equality, no parentheses required
result shouldBe 3       // cannot customize equality, so fastest to compile, no parentheses required

The “left should equal (right)” syntax requires an org.scalactic.Equality[L] to be provided (either implicitly or explicitly), where L is the left-hand type on which should is invoked. In the "left should equal (right)" case, for example, L is the type of left. Thus if left is type Int, the "left should equal (right)" statement would require an Equality[Int].

By default, an implicit Equality[T] instance is available for any type T, in which equality is implemented by simply invoking == on the left value, passing in the right value, with special treatment for arrays. If either left or right is an array, deep will be invoked on it before comparing with ==. Thus, the following expression will yield false, because Array's equals method compares object identity:

Array(1, 2) == Array(1, 2) // yields false

The next expression will by default not result in a TestFailedException, because default Equality[Array[Int]] compares the two arrays structurally, taking into consideration the equality of the array's contents:

Array(1, 2) should equal (Array(1, 2)) // succeeds (i.e., does not throw TestFailedException)

If you ever do want to verify that two arrays are actually the same object (have the same identity), you can use the be theSameInstanceAs syntax, described below.

You can customize the meaning of equality for a type when using "should equal," "should ===," or shouldEqual syntax by defining implicit Equality instances that will be used instead of default Equality. You might do this to normalize types before comparing them with ==, for instance, or to avoid calling the == method entirely, such as if you want to compare Doubles with a tolerance. For an example, see the main documentation of trait Equality.

You can always supply implicit parameters explicitly, but in the case of implicit parameters of type Equality[T], Scalactic provides a simple "explicitly" DSL. For example, here's how you could explicitly supply an Equality[String] instance that normalizes both left and right sides (which must be strings), by transforming them to lowercase:

scala> import org.scalatest.Matchers._
import org.scalatest.Matchers._

scala> import org.scalactic.Explicitly._
import org.scalactic.Explicitly._

scala> import org.scalactic.StringNormalizations._
import org.scalactic.StringNormalizations._

scala> "Hi" should equal ("hi") (after being lowerCased)

The after being lowerCased expression results in an Equality[String], which is then passed explicitly as the second curried parameter to equal. For more information on the explicitly DSL, see the main documentation for trait Explicitly.

The "should be" and shouldBe syntax do not take an Equality[T] and can therefore not be customized. They always use the default approach to equality described above. As a result, "should be" and shouldBe will likely be the fastest-compiling matcher syntax for equality comparisons, since the compiler need not search for an implicit Equality[T] each time.

The should === syntax (and its complement, should !==) can be used to enforce type constraints at compile-time between the left and right sides of the equality comparison. Here's an example:

scala> import org.scalatest.Matchers._
import org.scalatest.Matchers._

scala> import org.scalactic.TypeCheckedTripleEquals._
import org.scalactic.TypeCheckedTripleEquals._

scala> Some(2) should === (2)
<console>:17: error: types Some[Int] and Int do not adhere to the equality constraint
selected for the === and !== operators; the missing implicit parameter is of
type org.scalactic.CanEqual[Some[Int],Int]
              Some(2) should === (2)
                      ^

By default, the "Some(2) should === (2)" statement would fail at runtime. By mixing in the equality constraints provided by TypeCheckedTripleEquals, however, the statement fails to compile. For more information and examples, see the main documentation for trait TypeCheckedTripleEquals.

Checking size and length

You can check the size or length of any type of object for which it makes sense. Here's how checking for length looks:

result should have length 3

Size is similar:

result should have size 10

The length syntax can be used with String, Array, any scala.collection.GenSeq, any java.util.List, and any type T for which an implicit Length[T] type class is available in scope. Similarly, the size syntax can be used with Array, any scala.collection.GenTraversable, any java.util.Collection, any java.util.Map, and any type T for which an implicit Size[T] type class is available in scope. You can enable the length or size syntax for your own arbitrary types, therefore, by defining Length or Size type classes for those types.

In addition, the length syntax can be used with any object that has a field or method named length or a method named getLength. Similarly, the size syntax can be used with any object that has a field or method named size or a method named getSize. The type of a length or size field, or return type of a method, must be either Int or Long. Any such method must take no parameters. (The Scala compiler will ensure at compile time that the object on which should is being invoked has the appropriate structure.)

Checking strings

You can check for whether a string starts with, ends with, or includes a substring like this:

string should startWith ("Hello")
string should endWith ("world")
string should include ("seven")

You can check for whether a string starts with, ends with, or includes a regular expression, like this:

string should startWith regex "Hel*o"
string should endWith regex "wo.ld"
string should include regex "wo.ld"

And you can check whether a string fully matches a regular expression, like this:

string should fullyMatch regex """(-)?(\d+)(\.\d*)?"""

The regular expression passed following the regex token can be either a String or a scala.util.matching.Regex.

With the startWith, endWith, include, and fullyMatch tokens can also be used with an optional specification of required groups, like this:

"abbccxxx" should startWith regex ("a(b*)(c*)" withGroups ("bb", "cc"))
"xxxabbcc" should endWith regex ("a(b*)(c*)" withGroups ("bb", "cc"))
"xxxabbccxxx" should include regex ("a(b*)(c*)" withGroups ("bb", "cc"))
"abbcc" should fullyMatch regex ("a(b*)(c*)" withGroups ("bb", "cc"))

You can check whether a string is empty with empty:

s shouldBe empty

You can also use most of ScalaTest's matcher syntax for collections on String by treating the Strings as collections of characters. For examples, see the Strings and Arrays as collections section below.

Greater and less than

You can check whether any type for which an implicit Ordering[T] is available is greater than, less than, greater than or equal, or less than or equal to a value of type T. The syntax is:

one should be < 7
one should be > 0
one should be <= 7
one should be >= 0

Checking `Boolean` properties with `be`

If an object has a method that takes no parameters and returns boolean, you can check it by placing a Symbol (after be) that specifies the name of the method (excluding an optional prefix of "is"). A symbol literal in Scala begins with a tick mark and ends at the first non-identifier character. Thus, 'traversableAgain results in a Symbol object at runtime, as does 'completed and 'file. Here's an example:

iter shouldBe 'traversableAgain

Given this code, ScalaTest will use reflection to look on the object referenced from emptySet for a method that takes no parameters and results in Boolean, with either the name empty or isEmpty. If found, it will invoke that method. If the method returns true, execution will continue. But if it returns false, a TestFailedException will be thrown that will contain a detail message, such as:

non-empty iterator was not traversableAgain

This be syntax can be used with any reference (AnyRef) type. If the object does not have an appropriately named predicate method, you'll get a TestFailedException at runtime with a detailed message that explains the problem. (For the details on how a field or method is selected during this process, see the documentation for BeWord.)

If you think it reads better, you can optionally put a or an after be. For example, java.io.File has two predicate methods, isFile and isDirectory. Thus with a File object named temp, you could write:

temp should be a 'file

Or, given java.awt.event.KeyEvent has a method isActionKey that takes no arguments and returns Boolean, you could assert that a KeyEvent is an action key with:

keyEvent should be an 'actionKey

If you prefer to check Boolean properties in a type-safe manner, you can use a BePropertyMatcher. This would allow you to write expressions such as:

xs shouldBe traversableAgain
temp should be a file
keyEvent should be an actionKey

These expressions would fail to compile if should is used on an inappropriate type, as determined by the type parameter of the BePropertyMatcher being used. (For example, file in this example would likely be of type BePropertyMatcher[java.io.File]. If used with an appropriate type, such an expression will compile and at run time the Boolean property method or field will be accessed directly; i.e., no reflection will be used. See the documentation for BePropertyMatcher for more information.

Using custom `BeMatchers`

If you want to create a new way of using be, which doesn't map to an actual property on the type you care about, you can create a BeMatcher. You could use this, for example, to create BeMatcher[Int] called odd, which would match any odd Int, and even, which would match any even Int. Given this pair of BeMatchers, you could check whether an Int was odd or even with expressions like:

num shouldBe odd
num should not be even

For more information, see the documentation for BeMatcher.

Checking object identity

If you need to check that two references refer to the exact same object, you can write:

ref1 should be theSameInstanceAs ref2

Checking an object's class

If you need to check that an object is an instance of a particular class or trait, you can supply the type to “be a” or “be an”:

result1 shouldBe a [Tiger]
result1 should not be an [Orangutan]

Because type parameters are erased on the JVM, we recommend you insert an underscore for any type parameters when using this syntax. Both of the following test only that the result is an instance of List[_], because at runtime the type parameter has been erased:

result shouldBe a [List[_]] // recommended
result shouldBe a [List[Fruit]] // discouraged

Checking numbers against a range

Often you may want to check whether a number is within a range. You can do that using the +- operator, like this:

sevenDotOh should equal (6.9 +- 0.2)
sevenDotOh should === (6.9 +- 0.2)
sevenDotOh should be (6.9 +- 0.2)
sevenDotOh shouldEqual 6.9 +- 0.2
sevenDotOh shouldBe 6.9 +- 0.2

Any of these expressions will cause a TestFailedException to be thrown if the floating point value, sevenDotOh is outside the range 6.7 to 7.1. You can use +- with any type T for which an implicit Numeric[T] exists, such as integral types:

seven should equal (6 +- 2)
seven should === (6 +- 2)
seven should be (6 +- 2)
seven shouldEqual 6 +- 2
seven shouldBe 6 +- 2

Checking for emptiness

You can check whether an object is "empty", like this:

traversable shouldBe empty
javaMap should not be empty

The empty token can be used with any type L for which an implicit Emptiness[L] exists. The Emptiness companion object provides implicits for GenTraversable[E], java.util.Collection[E], java.util.Map[K, V], String, Array[E], and Option[E]. In addition, the Emptiness companion object provides structural implicits for types that declare an isEmpty method that returns a Boolean. Here are some examples:

scala> import org.scalatest.Matchers._
import org.scalatest.Matchers._

scala> List.empty shouldBe empty

scala> None shouldBe empty

scala> Some(1) should not be empty

scala> "" shouldBe empty

scala> new java.util.HashMap[Int, Int] shouldBe empty

scala> new { def isEmpty = true} shouldBe empty

scala> Array(1, 2, 3) should not be empty

Working with "containers"

You can check whether a collection contains a particular element like this:

traversable should contain ("five")

The contain syntax shown above can be used with any type C that has a "containing" nature, evidenced by an implicit org.scalatest.enablers.Containing[L], where L is left-hand type on which should is invoked. In the Containing companion object, implicits are provided for types GenTraversable[E], java.util.Collection[E], java.util.Map[K, V], String, Array[E], and Option[E]. Here are some examples:

scala> import org.scalatest.Matchers._
import org.scalatest.Matchers._

scala> List(1, 2, 3) should contain (2)

scala> Map('a' -> 1, 'b' -> 2, 'c' -> 3) should contain ('b' -> 2)

scala> Set(1, 2, 3) should contain (2)

scala> Array(1, 2, 3) should contain (2)

scala> "123" should contain ('2')

scala> Some(2) should contain (2)

ScalaTest's implicit methods that provide the Containing[L] type classes require an Equality[E], where E is an element type. For example, to obtain a Containing[Array[Int]] you must supply an Equality[Int], either implicitly or explicitly. The contain syntax uses this Equality[E] to determine containership. Thus if you want to change how containership is determined for an element type E, place an implicit Equality[E] in scope or use the explicitly DSL. Although the implicit parameter required for the contain syntax is of type Containing[L], implicit conversions are provided in the Containing companion object from Equality[E] to the various types of containers of E. Here's an example:

scala> import org.scalatest.Matchers._
import org.scalatest.Matchers._

scala> List("Hi", "Di", "Ho") should contain ("ho")
org.scalatest.exceptions.TestFailedException: List(Hi, Di, Ho) did not contain element "ho"
        at ...

scala> import org.scalactic.Explicitly._
import org.scalactic.Explicitly._

scala> import org.scalactic.StringNormalizations._
import org.scalactic.StringNormalizations._

scala> (List("Hi", "Di", "Ho") should contain ("ho")) (after being lowerCased)

Note that when you use the explicitly DSL with contain you need to wrap the entire contain expression in parentheses, as shown here.

(List("Hi", "Di", "Ho") should contain ("ho")) (after being lowerCased)
^                                            ^

In addition to determining whether an object contains another object, you can use contain to make other determinations. For example, the contain oneOf syntax ensures that one and only one of the specified elements are contained in the containing object:

List(1, 2, 3, 4, 5) should contain oneOf (5, 7, 9)
Some(7) should contain oneOf (5, 7, 9)
"howdy" should contain oneOf ('a', 'b', 'c', 'd')

Note that if multiple specified elements appear in the containing object, oneOf will fail:

scala> List(1, 2, 3) should contain oneOf (2, 3, 4)
org.scalatest.exceptions.TestFailedException: List(1, 2, 3) did not contain one (and only one) of (2, 3, 4)
        at ...

If you really want to ensure one or more of the specified elements are contained in the containing object, use atLeastOneOf, described below, instead of oneOf. Keep in mind, oneOf means "exactly one of."

Note also that with any contain syntax, you can place custom implicit Equality[E] instances in scope to customize how containership is determined, or use the explicitly DSL. Here's an example:

(Array("Doe", "Ray", "Me") should contain oneOf ("X", "RAY", "BEAM")) (after being lowerCased)

If you have a collection of elements that you'd like to use in a "one of" comparison, you can use "oneElementOf," like this:

List(1, 2, 3, 4, 5) should contain oneElementOf List(5, 7, 9)
Some(7) should contain oneElementOf Vector(5, 7, 9)
"howdy" should contain oneElementOf Set('a', 'b', 'c', 'd')
(Array("Doe", "Ray", "Me") should contain oneElementOf List("X", "RAY", "BEAM")) (after being lowerCased)

The contain noneOf syntax does the opposite of oneOf: it ensures none of the specified elements are contained in the containing object:

List(1, 2, 3, 4, 5) should contain noneOf (7, 8, 9)
Some(0) should contain noneOf (7, 8, 9)
"12345" should contain noneOf ('7', '8', '9')

If you have a collection of elements that you'd like to use in a "none of" comparison, you can use "noElementsOf," like this:

List(1, 2, 3, 4, 5) should contain noElementsOf List(7, 8, 9)
Some(0) should contain noElementsOf Vector(7, 8, 9)
"12345" should contain noElementsOf Set('7', '8', '9')

Working with "aggregations"

As mentioned, the "contain," "contain oneOf," and "contain noneOf" syntax requires a Containing[L] be provided, where L is the left-hand type. Other contain syntax, which will be described in this section, requires an Aggregating[L] be provided, where again L is the left-hand type. (An Aggregating[L] instance defines the "aggregating nature" of a type L.) The reason, essentially, is that contain syntax that makes sense for Option is enabled by Containing[L], whereas syntax that does not make sense for Option is enabled by Aggregating[L]. For example, it doesn't make sense to assert that an Option[Int] contains all of a set of integers, as it could only ever contain one of them. But this does make sense for a type such as List[Int] that can aggregate zero to many integers.

The Aggregating companion object provides implicit instances of Aggregating[L] for types GenTraversable[E], java.util.Collection[E], java.util.Map[K, V], String, Array[E]. Note that these are the same types as are supported with Containing, but with Option[E] missing. Here are some examples:

The contain atLeastOneOf syntax, for example, works for any type L for which an Aggregating[L] exists. It ensures that at least one of (i.e., one or more of) the specified objects are contained in the containing object:

List(1, 2, 3) should contain atLeastOneOf (2, 3, 4)
Array(1, 2, 3) should contain atLeastOneOf (3, 4, 5)
"abc" should contain atLeastOneOf ('c', 'a', 't')

Similar to Containing[L], the implicit methods that provide the Aggregating[L] instances require an Equality[E], where E is an element type. For example, to obtain a Aggregating[Vector[String]] you must supply an Equality[String], either implicitly or explicitly. The contain syntax uses this Equality[E] to determine containership. Thus if you want to change how containership is determined for an element type E, place an implicit Equality[E] in scope or use the explicitly DSL. Although the implicit parameter required for the contain syntax is of type Aggregating[L], implicit conversions are provided in the Aggregating companion object from Equality[E] to the various types of aggregations of E. Here's an example:

(Vector(" A", "B ") should contain atLeastOneOf ("a ", "b", "c")) (after being lowerCased and trimmed)

If you have a collection of elements that you'd like to use in an "at least one of" comparison, you can use "atLeastOneElementOf," like this:

List(1, 2, 3) should contain atLeastOneElementOf List(2, 3, 4)
Array(1, 2, 3) should contain atLeastOneElementOf Vector(3, 4, 5)
"abc" should contain atLeastOneElementOf Set('c', 'a', 't')
(Vector(" A", "B ") should contain atLeastOneElementOf List("a ", "b", "c")) (after being lowerCased and trimmed)

The "contain atMostOneOf" syntax lets you specify a set of objects at most one of which should be contained in the containing object:

List(1, 2, 3, 4, 5) should contain atMostOneOf (5, 6, 7)

If you have a collection of elements that you'd like to use in a "at most one of" comparison, you can use "atMostOneElementOf," like this:

List(1, 2, 3, 4, 5) should contain atMostOneElementOf Vector(5, 6, 7)

The "contain allOf" syntax lets you specify a set of objects that should all be contained in the containing object:

List(1, 2, 3, 4, 5) should contain allOf (2, 3, 5)

If you have a collection of elements that you'd like to use in a "all of" comparison, you can use "allElementsOf," like this:

List(1, 2, 3, 4, 5) should contain allElementsOf Array(2, 3, 5)

The "contain only" syntax lets you assert that the containing object contains only the specified objects, though it may contain more than one of each:

List(1, 2, 3, 2, 1) should contain only (1, 2, 3)

The "contain theSameElementsAs" and "contain theSameElementsInOrderAs syntax differ from the others in that the right hand side is a GenTraversable[_] rather than a varargs of Any. (Note: in a future 2.0 milestone release, possibly 2.0.M6, these will likely be widened to accept any type R for which an Aggregating[R] exists.)

The "contain theSameElementsAs" syntax lets you assert that two aggregations contain the same objects:

List(1, 2, 2, 3, 3, 3) should contain theSameElementsAs Vector(3, 2, 3, 1, 2, 3)

The number of times any family of equal objects appears must also be the same in both the left and right aggregations. The specified objects may appear multiple times, but must appear in the order they appear in the right-hand list. For example, if the last 3 element is left out of the right-hand list in the previous example, the expression would fail because the left side has three 3's and the right hand side has only two:

List(1, 2, 2, 3, 3, 3) should contain theSameElementsAs Vector(3, 2, 3, 1, 2)
org.scalatest.exceptions.TestFailedException: List(1, 2, 2, 3, 3, 3) did not contain the same elements as Vector(3, 2, 3, 1, 2)
        at ...

Note that no onlyElementsOf matcher is provided, because it would have the same behavior as theSameElementsAs. (I.e., if you were looking for onlyElementsOf, please use theSameElementsAs instead.)

Working with "sequences"

The rest of the contain syntax, which will be described in this section, requires a Sequencing[L] be provided, where again L is the left-hand type. (A Sequencing[L] instance defines the "sequencing nature" of a type L.) The reason, essentially, is that contain syntax that implies an "order" of elements makes sense only for types that place elements in a sequence. For example, it doesn't make sense to assert that a Map[String, Int] or Set[Int] contains all of a set of integers in a particular order, as these types don't necessarily define an order for their elements. But this does make sense for a type such as Seq[Int] that does define an order for its elements.

The Sequencing companion object provides implicit instances of Sequencing[L] for types GenSeq[E], java.util.List[E], String, and Array[E]. Here are some examples:

Similar to Containing[L], the implicit methods that provide the Aggregating[L] instances require an Equality[E], where E is an element type. For example, to obtain a Aggregating[Vector[String]] you must supply an Equality[String], either implicitly or explicitly. The contain syntax uses this Equality[E] to determine containership. Thus if you want to change how containership is determined for an element type E, place an implicit Equality[E] in scope or use the explicitly DSL. Although the implicit parameter required for the contain syntax is of type Aggregating[L], implicit conversions are provided in the Aggregating companion object from Equality[E] to the various types of aggregations of E. Here's an example:

The "contain inOrderOnly" syntax lets you assert that the containing object contains only the specified objects, in order. The specified objects may appear multiple times, but must appear in the order they appear in the right-hand list. Here's an example:

List(1, 2, 2, 3, 3, 3) should contain inOrderOnly (1, 2, 3)

The "contain inOrder" syntax lets you assert that the containing object contains only the specified objects in order, like inOrderOnly, but allows other objects to appear in the left-hand aggregation as well: contain more than one of each:

List(0, 1, 2, 2, 99, 3, 3, 3, 5) should contain inOrder (1, 2, 3)

If you have a collection of elements that you'd like to use in a "in order" comparison, you can use "inOrderElementsOf," like this:

List(0, 1, 2, 2, 99, 3, 3, 3, 5) should contain inOrderElementsOf Array(1, 2, 3)

Note that "order" in inOrder, inOrderOnly, and theSameElementsInOrderAs (described below) in the Aggregation[L] instances built-in to ScalaTest is defined as "iteration order".

Lastly, the "contain theSameElementsInOrderAs" syntax lets you assert that two aggregations contain the same exact elements in the same (iteration) order:

List(1, 2, 3) should contain theSameElementsInOrderAs collection.mutable.TreeSet(3, 2, 1)

The previous assertion succeeds because the iteration order of aTreeSet is the natural ordering of its elements, which in this case is 1, 2, 3. An iterator obtained from the left-hand List will produce the same elements in the same order.

Note that no inOrderOnlyElementsOf matcher is provided, because it would have the same behavior as theSameElementsInOrderAs. (I.e., if you were looking for inOrderOnlyElementsOf, please use theSameElementsInOrderAs instead.)

Working with "sortables"

You can also ask whether the elements of "sortable" objects (such as Arrays, Java Lists, and GenSeqs) are in sorted order, like this:

List(1, 2, 3) shouldBe sorted

Working with iterators

Although it seems desirable to provide similar matcher syntax for Scala and Java iterators to that provided for sequences like Seqs, Array, and java.util.List, the ephemeral nature of iterators makes this problematic. Some syntax (such as should contain) is relatively straightforward to support on iterators, but other syntax (such as, for example, Inspector expressions on nested iterators) is not. Rather than allowing inconsistencies between sequences and iterators in the API, we chose to not support any such syntax directly on iterators:

scala> val it = List(1, 2, 3).iterator
it: Iterator[Int] = non-empty iterator

scala> it should contain (2)
<console>:15: error: could not find implicit value for parameter typeClass1: org.scalatest.enablers.Containing[Iterator[Int]]
           it should contain (2)
              ^

Instead, you will need to convert your iterators to a sequence explicitly before using them in matcher expressions:

scala> it.toStream should contain (2)

We recommend you convert (Scala or Java) iterators to Streams, as shown in the previous example, so that you can continue to reap any potential benefits provided by the laziness of the underlying iterator.

Inspector shorthands

You can use the Inspectors syntax with matchers as well as assertions. If you have a multi-dimensional collection, such as a list of lists, using Inspectors is your best option:

val yss =
  List(
    List(1, 2, 3),
    List(1, 2, 3),
    List(1, 2, 3)
  )

forAll (yss) { ys =>
  forAll (ys) { y => y should be > 0 }
}

For assertions on one-dimensional collections, however, matchers provides "inspector shorthands." Instead of writing:

val xs = List(1, 2, 3)
forAll (xs) { x => x should be < 10 }

You can write:

all (xs) should be < 10

The previous statement asserts that all elements of the xs list should be less than 10. All of the inspectors have shorthands in matchers. Here is the full list:

all - succeeds if the assertion holds true for every element
atLeast - succeeds if the assertion holds true for at least the specified number of elements
atMost - succeeds if the assertion holds true for at most the specified number of elements
between - succeeds if the assertion holds true for between the specified minimum and maximum number of elements, inclusive
every - same as all, but lists all failing elements if it fails (whereas all just reports the first failing element)
exactly - succeeds if the assertion holds true for exactly the specified number of elements

Here are some examples:

scala> import org.scalatest.Matchers._
import org.scalatest.Matchers._

scala> val xs = List(1, 2, 3, 4, 5)
xs: List[Int] = List(1, 2, 3, 4, 5)

scala> all (xs) should be > 0

scala> atMost (2, xs) should be >= 4

scala> atLeast (3, xs) should be < 5

scala> between (2, 3, xs) should (be > 1 and be < 5)

scala> exactly (2, xs) should be <= 2

scala> every (xs) should be < 10

scala> // And one that fails...

scala> exactly (2, xs) shouldEqual 2
org.scalatest.exceptions.TestFailedException: 'exactly(2)' inspection failed, because only 1 element
    satisfied the assertion block at index 1:
  at index 0, 1 did not equal 2,
  at index 2, 3 did not equal 2,
  at index 3, 4 did not equal 2,
  at index 4, 5 did not equal 2
in List(1, 2, 3, 4, 5)
        at ...

Like Inspectors, objects used with inspector shorthands can be any type T for which a Collecting[T, E] is available, which by default includes GenTraversable, Java Collection, Java Map, Arrays, and Strings. Here are some examples:

scala> import org.scalatest._
import org.scalatest._

scala> import Matchers._
import Matchers._

scala> all (Array(1, 2, 3)) should be < 5

scala> import collection.JavaConverters._
import collection.JavaConverters._

scala> val js = List(1, 2, 3).asJava
js: java.util.List[Int] = [1, 2, 3]

scala> all (js) should be < 5

scala> val jmap = Map("a" -> 1, "b" -> 2).asJava
jmap: java.util.Map[String,Int] = {a=1, b=2}

scala> atLeast(1, jmap) shouldBe Entry("b", 2)

scala> atLeast(2, "hello, world!") shouldBe 'o'

Single-element collections

To assert both that a collection contains just one "lone" element as well as something else about that element, you can use the loneElement syntax provided by trait LoneElement. For example, if a Set[Int] should contain just one element, an Int less than or equal to 10, you could write:

import LoneElement._
set.loneElement should be <= 10

You can invoke loneElement on any type T for which an implicit Collecting[E, T] is available, where E is the element type returned by the loneElement invocation. By default, you can use loneElement on GenTraversable, Java Collection, Java Map, Array, and String.

Java collections and maps

You can use similar syntax on Java collections (java.util.Collection) and maps (java.util.Map). For example, you can check whether a Java Collection or Map is empty, like this:

javaCollection should be ('empty)
javaMap should be ('empty)

Even though Java's List type doesn't actually have a length or getLength method, you can nevertheless check the length of a Java List (java.util.List) like this:

javaList should have length 9

You can check the size of any Java Collection or Map, like this:

javaMap should have size 20
javaSet should have size 90

In addition, you can check whether a Java Collection contains a particular element, like this:

javaCollection should contain ("five")

One difference to note between the syntax supported on Java and Scala collections is that in Java, Map is not a subtype of Collection, and does not actually define an element type. You can ask a Java Map for an "entry set" via the entrySet method, which will return the Map's key/value pairs wrapped in a set of java.util.Map.Entry, but a Map is not actually a collection of Entry. To make Java Maps easier to work with, however, ScalaTest matchers allows you to treat a Java Map as a collection of Entry, and defines a convenience implementation of java.util.Map.Entry in org.scalatest.Entry. Here's how you use it:

javaMap should contain (Entry(2, 3))
javaMap should contain oneOf (Entry(2, 3), Entry(3, 4))

You can also just check whether a Java Map contains a particular key, or value, like this:

javaMap should contain key 1
javaMap should contain value "Howdy"

`String`s and `Array`s as collections

You can also use all the syntax described above for Scala and Java collections on Arrays and Strings. Here are some examples:

scala> import org.scalatest._
import org.scalatest._

scala> import Matchers._
import Matchers._

scala> atLeast (2, Array(1, 2, 3)) should be > 1

scala> atMost (2, "halloo") shouldBe 'o'

scala> Array(1, 2, 3) shouldBe sorted

scala> "abcdefg" shouldBe sorted

scala> Array(1, 2, 3) should contain atMostOneOf (3, 4, 5)

scala> "abc" should contain atMostOneOf ('c', 'd', 'e')

`be` as an equality comparison

All uses of be other than those shown previously perform an equality comparison. They work the same as equal when it is used with default equality. This redundancy between be and equals exists in part because it enables syntax that sometimes sounds more natural. For example, instead of writing:

result should equal (null)

You can write:

result should be (null)

(Hopefully you won't write that too much given null is error prone, and Option is usually a better, well, option.) As mentioned previously, the other difference between equal and be is that equal delegates the equality check to an Equality typeclass, whereas be always uses default equality. Here are some other examples of be used for equality comparison:

sum should be (7.0)
boring should be (false)
fun should be (true)
list should be (Nil)
option should be (None)
option should be (Some(1))

As with equal used with default equality, using be on arrays results in deep being called on both arrays prior to calling equal. As a result, the following expression would not throw a TestFailedException:

Array(1, 2) should be (Array(1, 2)) // succeeds (i.e., does not throw TestFailedException)

Because be is used in several ways in ScalaTest matcher syntax, just as it is used in many ways in English, one potential point of confusion in the event of a failure is determining whether be was being used as an equality comparison or in some other way, such as a property assertion. To make it more obvious when be is being used for equality, the failure messages generated for those equality checks will include the word equal in them. For example, if this expression fails with a TestFailedException:

option should be (Some(1))

The detail message in that TestFailedException will include the words "equal to" to signify be was in this case being used for equality comparison:

Some(2) was not equal to Some(1)

Being negative

If you wish to check the opposite of some condition, you can simply insert not in the expression. Here are a few examples:

result should not be (null)
sum should not be <= (10)
mylist should not equal (yourList)
string should not startWith ("Hello")

Checking that a snippet of code does not compile

Often when creating libraries you may wish to ensure that certain arrangements of code that represent potential “user errors” do not compile, so that your library is more error resistant. ScalaTest Matchers trait includes the following syntax for that purpose:

"val a: String = 1" shouldNot compile

If you want to ensure that a snippet of code does not compile because of a type error (as opposed to a syntax error), use:

"val a: String = 1" shouldNot typeCheck

Note that the shouldNot typeCheck syntax will only succeed if the given snippet of code does not compile because of a type error. A syntax error will still result in a thrown TestFailedException.

If you want to state that a snippet of code does compile, you can make that more obvious with:

"val a: Int = 1" should compile

Although the previous three constructs are implemented with macros that determine at compile time whether the snippet of code represented by the string does or does not compile, errors are reported as test failures at runtime.

Logical expressions with `and` and `or`

You can also combine matcher expressions with and and/or or, however, you must place parentheses or curly braces around the and or or expression. For example, this and-expression would not compile, because the parentheses are missing:

map should contain key ("two") and not contain value (7) // ERROR, parentheses missing!

Instead, you need to write:

map should (contain key ("two") and not contain value (7))

Here are some more examples:

number should (be > (0) and be <= (10))
option should (equal (Some(List(1, 2, 3))) or be (None))
string should (
  equal ("fee") or
  equal ("fie") or
  equal ("foe") or
  equal ("fum")
)

Two differences exist between expressions composed of these and and or operators and the expressions you can write on regular Booleans using its && and || operators. First, expressions with and and or do not short-circuit. The following contrived expression, for example, would print "hello, world!":

"yellow" should (equal ("blue") and equal { println("hello, world!"); "green" })

In other words, the entire and or or expression is always evaluated, so you'll see any side effects of the right-hand side even if evaluating only the left-hand side is enough to determine the ultimate result of the larger expression. Failure messages produced by these expressions will "short-circuit," however, mentioning only the left-hand side if that's enough to determine the result of the entire expression. This "short-circuiting" behavior of failure messages is intended to make it easier and quicker for you to ascertain which part of the expression caused the failure. The failure message for the previous expression, for example, would be:

"yellow" did not equal "blue"

Most likely this lack of short-circuiting would rarely be noticeable, because evaluating the right hand side will usually not involve a side effect. One situation where it might show up, however, is if you attempt to and a null check on a variable with an expression that uses the variable, like this:

map should (not be (null) and contain key ("ouch"))

If map is null, the test will indeed fail, but with a NullArgumentException, not a TestFailedException. Here, the NullArgumentException is the visible right-hand side effect. To get a TestFailedException, you would need to check each assertion separately:

map should not be (null)
map should contain key ("ouch")

If map is null in this case, the null check in the first expression will fail with a TestFailedException, and the second expression will never be executed.

The other difference with Boolean operators is that although && has a higher precedence than ||, and and or have the same precedence. Thus although the Boolean expression (a || b && c) will evaluate the && expression before the || expression, like (a || (b && c)), the following expression:

traversable should (contain (7) or contain (8) and have size (9))

Will evaluate left to right, as:

traversable should ((contain (7) or contain (8)) and have size (9))

If you really want the and part to be evaluated first, you'll need to put in parentheses, like this:

traversable should (contain (7) or (contain (8) and have size (9)))

Working with `Option`s

You can work with options using ScalaTest's equality, empty, defined, and contain syntax. For example, if you wish to check whether an option is None, you can write any of:

option shouldEqual None
option shouldBe None
option should === (None)
option shouldBe empty

If you wish to check an option is defined, and holds a specific value, you can write any of:

option shouldEqual Some("hi")
option shouldBe Some("hi")
option should === (Some("hi"))

If you only wish to check that an option is defined, but don't care what it's value is, you can write:

option shouldBe defined

If you mix in (or import the members of) OptionValues, you can write one statement that indicates you believe an option should be defined and then say something else about its value. Here's an example:

import org.scalatest.OptionValues._
option.value should be < 7

As mentioned previously, you can use also use ScalaTest's contain, contain oneOf, and contain noneOf syntax with options:

Some(2) should contain (2)
Some(7) should contain oneOf (5, 7, 9)
Some(0) should contain noneOf (7, 8, 9)

Checking arbitrary properties with `have`

Using have, you can check properties of any type, where a property is an attribute of any object that can be retrieved either by a public field, method, or JavaBean-style get or is method, like this:

book should have (
  'title ("Programming in Scala"),
  'author (List("Odersky", "Spoon", "Venners")),
  'pubYear (2008)
)

This expression will use reflection to ensure the title, author, and pubYear properties of object book are equal to the specified values. For example, it will ensure that book has either a public Java field or method named title, or a public method named getTitle, that when invoked (or accessed in the field case) results in the string "Programming in Scala". If all specified properties exist and have their expected values, respectively, execution will continue. If one or more of the properties either does not exist, or exists but results in an unexpected value, a TestFailedException will be thrown that explains the problem. (For the details on how a field or method is selected during this process, see the documentation for HavePropertyMatcherGenerator.)

When you use this syntax, you must place one or more property values in parentheses after have, separated by commas, where a property value is a symbol indicating the name of the property followed by the expected value in parentheses. The only exceptions to this rule is the syntax for checking size and length shown previously, which does not require parentheses. If you forget and put parentheses in, however, everything will still work as you'd expect. Thus instead of writing:

array should have length (3)
set should have size (90)

You can alternatively, write:

array should have (length (3))
set should have (size (90))

If a property has a value different from the specified expected value, a TestFailedError will be thrown with a detailed message that explains the problem. For example, if you assert the following on a book whose title is Moby Dick:

book should have ('title ("A Tale of Two Cities"))

You'll get a TestFailedException with this detail message:

The title property had value "Moby Dick", instead of its expected value "A Tale of Two Cities",
on object Book("Moby Dick", "Melville", 1851)

If you prefer to check properties in a type-safe manner, you can use a HavePropertyMatcher. This would allow you to write expressions such as:

book should have (
  title ("Programming in Scala"),
  author (List("Odersky", "Spoon", "Venners")),
  pubYear (2008)
)

These expressions would fail to compile if should is used on an inappropriate type, as determined by the type parameter of the HavePropertyMatcher being used. (For example, title in this example might be of type HavePropertyMatcher[org.publiclibrary.Book]. If used with an appropriate type, such an expression will compile and at run time the property method or field will be accessed directly; i.e., no reflection will be used. See the documentation for HavePropertyMatcher for more information.

Using `length` and `size` with `HavePropertyMatcher`s

If you want to use length or size syntax with your own custom HavePropertyMatchers, you can do so, but you must write (of [“the type”]) afterwords. For example, you could write:

book should have (
  title ("A Tale of Two Cities"),
  length (220) (of [Book]),
  author ("Dickens")
)

Prior to ScalaTest 2.0, “length (22)” yielded a HavePropertyMatcher[Any, Int] that used reflection to dynamically look for a length field or getLength method. In ScalaTest 2.0, “length (22)” yields a MatcherFactory1[Any, Length], so it is no longer a HavePropertyMatcher. The (of [<type>]) syntax converts the the MatcherFactory1[Any, Length] to a HavePropertyMatcher[<type>, Int].

Checking that an expression matches a pattern

ScalaTest's Inside trait allows you to make assertions after a pattern match. Here's an example:

case class Name(first: String, middle: String, last: String)

val name = Name("Jane", "Q", "Programmer")

inside(name) { case Name(first, _, _) =>
  first should startWith ("S")
}

You can use inside to just ensure a pattern is matched, without making any further assertions, but a better alternative for that kind of assertion is matchPattern. The matchPattern syntax allows you to express that you expect a value to match a particular pattern, no more and no less:

name should matchPattern { case Name("Sarah", _, _) => }

Using custom matchers

If none of the built-in matcher syntax (or options shown so far for extending the syntax) satisfy a particular need you have, you can create custom Matchers that allow you to place your own syntax directly after should. For example, class java.io.File has a method isHidden, which indicates whether a file of a certain path and name is hidden. Because the isHidden method takes no parameters and returns Boolean, you can call it using be with a symbol or BePropertyMatcher, yielding assertions like:

file should be ('hidden)  // using a symbol
file should be (hidden)   // using a BePropertyMatcher

If it doesn't make sense to have your custom syntax follow be, you might want to create a custom Matcher instead, so your syntax can follow should directly. For example, you might want to be able to check whether a java.io.File's name ends with a particular extension, like this:

// using a plain-old Matcher
file should endWithExtension ("txt")

ScalaTest provides several mechanism to make it easy to create custom matchers, including ways to compose new matchers out of existing ones complete with new error messages. For more information about how to create custom Matchers, please see the documentation for the Matcher trait.

Checking for expected exceptions

Sometimes you need to test whether a method throws an expected exception under certain circumstances, such as when invalid arguments are passed to the method. With Matchers mixed in, you can check for an expected exception like this:

an [IndexOutOfBoundsException] should be thrownBy s.charAt(-1)

If charAt throws an instance of StringIndexOutOfBoundsException, this expression will result in that exception. But if charAt completes normally, or throws a different exception, this expression will complete abruptly with a TestFailedException.

If you need to further inspect an expected exception, you can capture it using this syntax:

val thrown = the [IndexOutOfBoundsException] thrownBy s.charAt(-1)

This expression returns the caught exception so that you can inspect it further if you wish, for example, to ensure that data contained inside the exception has the expected values. Here's an example:

thrown.getMessage should equal ("String index out of range: -1")

If you prefer you can also capture and inspect an expected exception in one statement, like this:

the [ArithmeticException] thrownBy 1 / 0 should have message "/ by zero"
the [IndexOutOfBoundsException] thrownBy {
  s.charAt(-1)
} should have message "String index out of range: -1"

You can also state that no exception should be thrown by some code, like this:

noException should be thrownBy 0 / 1

Those pesky parens

Perhaps the most tricky part of writing assertions using ScalaTest matchers is remembering when you need or don't need parentheses, but bearing in mind a few simple rules should help. It is also reassuring to know that if you ever leave off a set of parentheses when they are required, your code will not compile. Thus the compiler will help you remember when you need the parens. That said, the rules are:

1. Although you don't always need them, you may choose to always put parentheses around right-hand values, such as the 7 in num should equal (7):

result should equal (4)
array should have length (3)
book should have (
  'title ("Programming in Scala"),
  'author (List("Odersky", "Spoon", "Venners")),
  'pubYear (2008)
)
option should be ('defined)
catMap should (contain key (9) and contain value ("lives"))
keyEvent should be an ('actionKey)
javaSet should have size (90)

2. Except for length, size and message, you must always put parentheses around the list of one or more property values following a have:

file should (exist and have ('name ("temp.txt")))
book should have (
  title ("Programming in Scala"),
  author (List("Odersky", "Spoon", "Venners")),
  pubYear (2008)
)
javaList should have length (9) // parens optional for length and size

3. You must always put parentheses around and and or expressions, as in:

catMap should (contain key (9) and contain value ("lives"))
number should (equal (2) or equal (4) or equal (8))

4. Although you don't always need them, you may choose to always put parentheses around custom Matchers when they appear directly after not:

file should exist
file should not (exist)
file should (exist and have ('name ("temp.txt")))
file should (not (exist) and have ('name ("temp.txt"))
file should (have ('name ("temp.txt") or exist)
file should (have ('name ("temp.txt") or not (exist))

That's it. With a bit of practice it should become natural to you, and the compiler will always be there to tell you if you forget a set of needed parentheses.

Note: ScalaTest's matchers are in part inspired by the matchers of RSpec, Hamcrest, and specs2, and its “shouldNot compile” syntax by the illTyped macro of shapeless.

trait MustMatchers extends Assertions with Tolerance with MustVerb with MatcherWords with Explicitly

Trait that provides a domain specific language (DSL) for expressing assertions in tests using the word must.

For example, if you mix Matchers into a suite class, you can write an equality assertion in that suite like this:

result must equal (3)

Here result is a variable, and can be of any type. If the object is an Int with the value 3, execution will continue (i.e., the expression will result in the unit value, ()). Otherwise, a TestFailedException will be thrown with a detail message that explains the problem, such as "7 did not equal 3". This TestFailedException will cause the test to fail.

Here is a table of contents for this documentation:

Matchers migration in ScalaTest 2.0
Checking equality with matchers
Checking size and length
Checking strings
Greater and less than
Checking Boolean properties with be
Using custom BeMatchers
Checking object identity
Checking an object's class
Checking numbers against a range
Checking for emptiness
Working with "containers"
Working with "aggregations"
Working with "sequences"
Working with "sortables"
Working with iterators
Inspector shorthands
Single-element collections
Java collections and maps
Strings and Arrays as collections
Be as an equality comparison
Being negative
Checking that a snippet of code does not compile
Logical expressions with and and or
Working with Options
Checking arbitrary properties with have
Using length and size with HavePropertyMatchers
Checking that an expression matches a pattern
Using custom matchers
Checking for expected exceptions
Those pesky parens

Trait MustMatchers is an alternative to Matchers that provides the exact same meaning, syntax, and behavior as Matchers, but uses the verb must instead of should. The two traits differ only in the English semantics of the verb: should is informal, making the code feel like conversation between the writer and the reader; must is more formal, making the code feel more like a written specification.

Checking equality with matchers

ScalaTest matchers provides five different ways to check equality, each designed to address a different need. They are:

result must equal (3) // can customize equality
result must === (3)   // can customize equality and enforce type constraints
result must be (3)    // cannot customize equality, so fastest to compile
result mustEqual 3    // can customize equality, no parentheses required
result mustBe 3       // cannot customize equality, so fastest to compile, no parentheses required

The “left must equal (right)” syntax requires an org.scalactic.Equality[L] to be provided (either implicitly or explicitly), where L is the left-hand type on which must is invoked. In the "left must equal (right)" case, for example, L is the type of left. Thus if left is type Int, the "left must equal (right)" statement would require an Equality[Int].

By default, an implicit Equality[T] instance is available for any type T, in which equality is implemented by simply invoking == on the left value, passing in the right value, with special treatment for arrays. If either left or right is an array, deep will be invoked on it before comparing with ==. Thus, the following expression will yield false, because Array's equals method compares object identity:

Array(1, 2) == Array(1, 2) // yields false

The next expression will by default not result in a TestFailedException, because default Equality[Array[Int]] compares the two arrays structurally, taking into consideration the equality of the array's contents:

Array(1, 2) must equal (Array(1, 2)) // succeeds (i.e., does not throw TestFailedException)

If you ever do want to verify that two arrays are actually the same object (have the same identity), you can use the be theSameInstanceAs syntax, described below.

You can customize the meaning of equality for a type when using "must equal," "must ===," or mustEqual syntax by defining implicit Equality instances that will be used instead of default Equality. You might do this to normalize types before comparing them with ==, for instance, or to avoid calling the == method entirely, such as if you want to compare Doubles with a tolerance. For an example, see the main documentation of trait Equality.

You can always supply implicit parameters explicitly, but in the case of implicit parameters of type Equality[T], Scalactic provides a simple "explicitly" DSL. For example, here's how you could explicitly supply an Equality[String] instance that normalizes both left and right sides (which must be strings), by transforming them to lowercase:

scala> import org.scalatest.MustMatchers._
import org.scalatest.MustMatchers._

scala> import org.scalactic.Explicitly._
import org.scalactic.Explicitly._

scala> import org.scalactic.StringNormalizations._
import org.scalactic.StringNormalizations._

scala> "Hi" must equal ("hi") (after being lowerCased)

The after being lowerCased expression results in an Equality[String], which is then passed explicitly as the second curried parameter to equal. For more information on the explicitly DSL, see the main documentation for trait Explicitly.

The "must be" and mustBe syntax do not take an Equality[T] and can therefore not be customized. They always use the default approach to equality described above. As a result, "must be" and mustBe will likely be the fastest-compiling matcher syntax for equality comparisons, since the compiler need not search for an implicit Equality[T] each time.

The must === syntax (and its complement, must !==) can be used to enforce type constraints at compile-time between the left and right sides of the equality comparison. Here's an example:

scala> import org.scalatest.MustMatchers._
import org.scalatest.MustMatchers._

scala> import org.scalactic.TypeCheckedTripleEquals._
import org.scalactic.TypeCheckedTripleEquals._

scala> Some(2) must === (2)
<console>:17: error: types Some[Int] and Int do not adhere to the equality constraint
selected for the === and !== operators; the missing implicit parameter is of
type org.scalactic.CanEqual[Some[Int],Int]
              Some(2) must === (2)
                      ^

By default, the "Some(2) must === (2)" statement would fail at runtime. By mixing in the equality constraints provided by TypeCheckedTripleEquals, however, the statement fails to compile. For more information and examples, see the main documentation for trait TypeCheckedTripleEquals.

Checking size and length

You can check the size or length of any type of object for which it makes sense. Here's how checking for length looks:

result must have length 3

Size is similar:

result must have size 10

The length syntax can be used with String, Array, any scala.collection.GenSeq, any java.util.List, and any type T for which an implicit Length[T] type class is available in scope. Similarly, the size syntax can be used with Array, any scala.collection.GenTraversable, any java.util.Collection, any java.util.Map, and any type T for which an implicit Size[T] type class is available in scope. You can enable the length or size syntax for your own arbitrary types, therefore, by defining Length or Size type classes for those types.

In addition, the length syntax can be used with any object that has a field or method named length or a method named getLength. Similarly, the size syntax can be used with any object that has a field or method named size or a method named getSize. The type of a length or size field, or return type of a method, must be either Int or Long. Any such method must take no parameters. (The Scala compiler will ensure at compile time that the object on which must is being invoked has the appropriate structure.)

Checking strings

You can check for whether a string starts with, ends with, or includes a substring like this:

string must startWith ("Hello")
string must endWith ("world")
string must include ("seven")

You can check for whether a string starts with, ends with, or includes a regular expression, like this:

string must startWith regex "Hel*o"
string must endWith regex "wo.ld"
string must include regex "wo.ld"

And you can check whether a string fully matches a regular expression, like this:

string must fullyMatch regex """(-)?(\d+)(\.\d*)?"""

The regular expression passed following the regex token can be either a String or a scala.util.matching.Regex.

With the startWith, endWith, include, and fullyMatch tokens can also be used with an optional specification of required groups, like this:

"abbccxxx" must startWith regex ("a(b*)(c*)" withGroups ("bb", "cc"))
"xxxabbcc" must endWith regex ("a(b*)(c*)" withGroups ("bb", "cc"))
"xxxabbccxxx" must include regex ("a(b*)(c*)" withGroups ("bb", "cc"))
"abbcc" must fullyMatch regex ("a(b*)(c*)" withGroups ("bb", "cc"))

You can check whether a string is empty with empty:

s mustBe empty

You can also use most of ScalaTest's matcher syntax for collections on String by treating the Strings as collections of characters. For examples, see the Strings and Arrays as collections section below.

Greater and less than

You can check whether any type for which an implicit Ordering[T] is available is greater than, less than, greater than or equal, or less than or equal to a value of type T. The syntax is:

one must be < 7
one must be > 0
one must be <= 7
one must be >= 0

Checking `Boolean` properties with `be`

If an object has a method that takes no parameters and returns boolean, you can check it by placing a Symbol (after be) that specifies the name of the method (excluding an optional prefix of "is"). A symbol literal in Scala begins with a tick mark and ends at the first non-identifier character. Thus, 'traversableAgain results in a Symbol object at runtime, as does 'completed and 'file. Here's an example:

iter mustBe 'traversableAgain

Given this code, ScalaTest will use reflection to look on the object referenced from emptySet for a method that takes no parameters and results in Boolean, with either the name empty or isEmpty. If found, it will invoke that method. If the method returns true, execution will continue. But if it returns false, a TestFailedException will be thrown that will contain a detail message, such as:

non-empty iterator was not traversableAgain

This be syntax can be used with any reference (AnyRef) type. If the object does not have an appropriately named predicate method, you'll get a TestFailedException at runtime with a detailed message that explains the problem. (For the details on how a field or method is selected during this process, see the documentation for BeWord.)

If you think it reads better, you can optionally put a or an after be. For example, java.io.File has two predicate methods, isFile and isDirectory. Thus with a File object named temp, you could write:

temp must be a 'file

Or, given java.awt.event.KeyEvent has a method isActionKey that takes no arguments and returns Boolean, you could assert that a KeyEvent is an action key with:

keyEvent must be an 'actionKey

If you prefer to check Boolean properties in a type-safe manner, you can use a BePropertyMatcher. This would allow you to write expressions such as:

xs mustBe traversableAgain
temp must be a file
keyEvent must be an actionKey

These expressions would fail to compile if must is used on an inappropriate type, as determined by the type parameter of the BePropertyMatcher being used. (For example, file in this example would likely be of type BePropertyMatcher[java.io.File]. If used with an appropriate type, such an expression will compile and at run time the Boolean property method or field will be accessed directly; i.e., no reflection will be used. See the documentation for BePropertyMatcher for more information.

Using custom `BeMatchers`

If you want to create a new way of using be, which doesn't map to an actual property on the type you care about, you can create a BeMatcher. You could use this, for example, to create BeMatcher[Int] called odd, which would match any odd Int, and even, which would match any even Int. Given this pair of BeMatchers, you could check whether an Int was odd or even with expressions like:

num mustBe odd
num must not be even

For more information, see the documentation for BeMatcher.

Checking object identity

If you need to check that two references refer to the exact same object, you can write:

ref1 must be theSameInstanceAs ref2

Checking an object's class

If you need to check that an object is an instance of a particular class or trait, you can supply the type to “be a” or “be an”:

result1 mustBe a [Tiger]
result1 must not be an [Orangutan]

Because type parameters are erased on the JVM, we recommend you insert an underscore for any type parameters when using this syntax. Both of the following test only that the result is an instance of List[_], because at runtime the type parameter has been erased:

result mustBe a [List[_]] // recommended
result mustBe a [List[Fruit]] // discouraged

Checking numbers against a range

Often you may want to check whether a number is within a range. You can do that using the +- operator, like this:

sevenDotOh must equal (6.9 +- 0.2)
sevenDotOh must === (6.9 +- 0.2)
sevenDotOh must be (6.9 +- 0.2)
sevenDotOh mustEqual 6.9 +- 0.2
sevenDotOh mustBe 6.9 +- 0.2

Any of these expressions will cause a TestFailedException to be thrown if the floating point value, sevenDotOh is outside the range 6.7 to 7.1. You can use +- with any type T for which an implicit Numeric[T] exists, such as integral types:

seven must equal (6 +- 2)
seven must === (6 +- 2)
seven must be (6 +- 2)
seven mustEqual 6 +- 2
seven mustBe 6 +- 2

Checking for emptiness

You can check whether an object is "empty", like this:

traversable mustBe empty
javaMap must not be empty

The empty token can be used with any type L for which an implicit Emptiness[L] exists. The Emptiness companion object provides implicits for GenTraversable[E], java.util.Collection[E], java.util.Map[K, V], String, Array[E], and Option[E]. In addition, the Emptiness companion object provides structural implicits for types that declare an isEmpty method that returns a Boolean. Here are some examples:

scala> import org.scalatest.MustMatchers._
import org.scalatest.MustMatchers._

scala> List.empty mustBe empty

scala> None mustBe empty

scala> Some(1) must not be empty

scala> "" mustBe empty

scala> new java.util.HashMap[Int, Int] mustBe empty

scala> new { def isEmpty = true} mustBe empty

scala> Array(1, 2, 3) must not be empty

Working with "containers"

You can check whether a collection contains a particular element like this:

traversable must contain ("five")

The contain syntax shown above can be used with any type C that has a "containing" nature, evidenced by an implicit org.scalatest.enablers.Containing[L], where L is left-hand type on which must is invoked. In the Containing companion object, implicits are provided for types GenTraversable[E], java.util.Collection[E], java.util.Map[K, V], String, Array[E], and Option[E]. Here are some examples:

scala> import org.scalatest.MustMatchers._
import org.scalatest.MustMatchers._

scala> List(1, 2, 3) must contain (2)

scala> Map('a' -> 1, 'b' -> 2, 'c' -> 3) must contain ('b' -> 2)

scala> Set(1, 2, 3) must contain (2)

scala> Array(1, 2, 3) must contain (2)

scala> "123" must contain ('2')

scala> Some(2) must contain (2)

ScalaTest's implicit methods that provide the Containing[L] type classes require an Equality[E], where E is an element type. For example, to obtain a Containing[Array[Int]] you must supply an Equality[Int], either implicitly or explicitly. The contain syntax uses this Equality[E] to determine containership. Thus if you want to change how containership is determined for an element type E, place an implicit Equality[E] in scope or use the explicitly DSL. Although the implicit parameter required for the contain syntax is of type Containing[L], implicit conversions are provided in the Containing companion object from Equality[E] to the various types of containers of E. Here's an example:

scala> import org.scalatest.MustMatchers._
import org.scalatest.MustMatchers._

scala> List("Hi", "Di", "Ho") must contain ("ho")
org.scalatest.exceptions.TestFailedException: List(Hi, Di, Ho) did not contain element "ho"
        at ...

scala> import org.scalactic.Explicitly._
import org.scalactic.Explicitly._

scala> import org.scalactic.StringNormalizations._
import org.scalactic.StringNormalizations._

scala> (List("Hi", "Di", "Ho") must contain ("ho")) (after being lowerCased)

Note that when you use the explicitly DSL with contain you need to wrap the entire contain expression in parentheses, as shown here.

(List("Hi", "Di", "Ho") must contain ("ho")) (after being lowerCased)
^                                            ^

In addition to determining whether an object contains another object, you can use contain to make other determinations. For example, the contain oneOf syntax ensures that one and only one of the specified elements are contained in the containing object:

List(1, 2, 3, 4, 5) must contain oneOf (5, 7, 9)
Some(7) must contain oneOf (5, 7, 9)
"howdy" must contain oneOf ('a', 'b', 'c', 'd')

Note that if multiple specified elements appear in the containing object, oneOf will fail:

scala> List(1, 2, 3) must contain oneOf (2, 3, 4)
org.scalatest.exceptions.TestFailedException: List(1, 2, 3) did not contain one (and only one) of (2, 3, 4)
        at ...

If you really want to ensure one or more of the specified elements are contained in the containing object, use atLeastOneOf, described below, instead of oneOf. Keep in mind, oneOf means "exactly one of."

Note also that with any contain syntax, you can place custom implicit Equality[E] instances in scope to customize how containership is determined, or use the explicitly DSL. Here's an example:

(Array("Doe", "Ray", "Me") must contain oneOf ("X", "RAY", "BEAM")) (after being lowerCased)

If you have a collection of elements that you'd like to use in a "one of" comparison, you can use "oneElementOf," like this:

List(1, 2, 3, 4, 5) must contain oneElementOf List(5, 7, 9)
Some(7) must contain oneElementOf Vector(5, 7, 9)
"howdy" must contain oneElementOf Set('a', 'b', 'c', 'd')
(Array("Doe", "Ray", "Me") must contain oneElementOf List("X", "RAY", "BEAM")) (after being lowerCased)

The contain noneOf syntax does the opposite of oneOf: it ensures none of the specified elements are contained in the containing object:

List(1, 2, 3, 4, 5) must contain noneOf (7, 8, 9)
Some(0) must contain noneOf (7, 8, 9)
"12345" must contain noneOf ('7', '8', '9')

If you have a collection of elements that you'd like to use in a "none of" comparison, you can use "noElementsOf," like this:

List(1, 2, 3, 4, 5) must contain noElementsOf List(7, 8, 9)
Some(0) must contain noElementsOf Vector(7, 8, 9)
"12345" must contain noElementsOf Set('7', '8', '9')

Working with "aggregations"

As mentioned, the "contain," "contain oneOf," and "contain noneOf" syntax requires a Containing[L] be provided, where L is the left-hand type. Other contain syntax, which will be described in this section, requires an Aggregating[L] be provided, where again L is the left-hand type. (An Aggregating[L] instance defines the "aggregating nature" of a type L.) The reason, essentially, is that contain syntax that makes sense for Option is enabled by Containing[L], whereas syntax that does not make sense for Option is enabled by Aggregating[L]. For example, it doesn't make sense to assert that an Option[Int] contains all of a set of integers, as it could only ever contain one of them. But this does make sense for a type such as List[Int] that can aggregate zero to many integers.

The Aggregating companion object provides implicit instances of Aggregating[L] for types GenTraversable[E], java.util.Collection[E], java.util.Map[K, V], String, Array[E]. Note that these are the same types as are supported with Containing, but with Option[E] missing. Here are some examples:

The contain atLeastOneOf syntax, for example, works for any type L for which an Aggregating[L] exists. It ensures that at least one of (i.e., one or more of) the specified objects are contained in the containing object:

List(1, 2, 3) must contain atLeastOneOf (2, 3, 4)
Array(1, 2, 3) must contain atLeastOneOf (3, 4, 5)
"abc" must contain atLeastOneOf ('c', 'a', 't')

Similar to Containing[L], the implicit methods that provide the Aggregating[L] instances require an Equality[E], where E is an element type. For example, to obtain a Aggregating[Vector[String]] you must supply an Equality[String], either implicitly or explicitly. The contain syntax uses this Equality[E] to determine containership. Thus if you want to change how containership is determined for an element type E, place an implicit Equality[E] in scope or use the explicitly DSL. Although the implicit parameter required for the contain syntax is of type Aggregating[L], implicit conversions are provided in the Aggregating companion object from Equality[E] to the various types of aggregations of E. Here's an example:

(Vector(" A", "B ") must contain atLeastOneOf ("a ", "b", "c")) (after being lowerCased and trimmed)

If you have a collection of elements that you'd like to use in an "at least one of" comparison, you can use "atLeastOneElementOf," like this:

List(1, 2, 3) must contain atLeastOneElementOf List(2, 3, 4)
Array(1, 2, 3) must contain atLeastOneElementOf Vector(3, 4, 5)
"abc" must contain atLeastOneElementOf Set('c', 'a', 't')
(Vector(" A", "B ") must contain atLeastOneElementOf List("a ", "b", "c")) (after being lowerCased and trimmed)

The "contain atMostOneOf" syntax lets you specify a set of objects at most one of which must be contained in the containing object:

List(1, 2, 3, 4, 5) must contain atMostOneOf (5, 6, 7)

If you have a collection of elements that you'd like to use in a "at most one of" comparison, you can use "atMostOneElementOf," like this:

List(1, 2, 3, 4, 5) must contain atMostOneElementOf Vector(5, 6, 7)

The "contain allOf" syntax lets you specify a set of objects that must all be contained in the containing object:

List(1, 2, 3, 4, 5) must contain allOf (2, 3, 5)

If you have a collection of elements that you'd like to use in a "all of" comparison, you can use "allElementsOf," like this:

List(1, 2, 3, 4, 5) must contain allElementsOf Array(2, 3, 5)

The "contain only" syntax lets you assert that the containing object contains only the specified objects, though it may contain more than one of each:

List(1, 2, 3, 2, 1) must contain only (1, 2, 3)

The "contain theSameElementsAs" and "contain theSameElementsInOrderAs syntax differ from the others in that the right hand side is a GenTraversable[_] rather than a varargs of Any. (Note: in a future 2.0 milestone release, possibly 2.0.M6, these will likely be widened to accept any type R for which an Aggregating[R] exists.)

The "contain theSameElementsAs" syntax lets you assert that two aggregations contain the same objects:

List(1, 2, 2, 3, 3, 3) must contain theSameElementsAs Vector(3, 2, 3, 1, 2, 3)

The number of times any family of equal objects appears must also be the same in both the left and right aggregations. The specified objects may appear multiple times, but must appear in the order they appear in the right-hand list. For example, if the last 3 element is left out of the right-hand list in the previous example, the expression would fail because the left side has three 3's and the right hand side has only two:

List(1, 2, 2, 3, 3, 3) must contain theSameElementsAs Vector(3, 2, 3, 1, 2)
org.scalatest.exceptions.TestFailedException: List(1, 2, 2, 3, 3, 3) did not contain the same elements as Vector(3, 2, 3, 1, 2)
        at ...

Note that no onlyElementsOf matcher is provided, because it would have the same behavior as theSameElementsAs. (I.e., if you were looking for onlyElementsOf, please use theSameElementsAs instead.)

Working with "sequences"

The rest of the contain syntax, which will be described in this section, requires a Sequencing[L] be provided, where again L is the left-hand type. (A Sequencing[L] instance defines the "sequencing nature" of a type L.) The reason, essentially, is that contain syntax that implies an "order" of elements makes sense only for types that place elements in a sequence. For example, it doesn't make sense to assert that a Map[String, Int] or Set[Int] contains all of a set of integers in a particular order, as these types don't necessarily define an order for their elements. But this does make sense for a type such as Seq[Int] that does define an order for its elements.

The Sequencing companion object provides implicit instances of Sequencing[L] for types GenSeq[E], java.util.List[E], String, and Array[E]. Here are some examples:

Similar to Containing[L], the implicit methods that provide the Aggregating[L] instances require an Equality[E], where E is an element type. For example, to obtain a Aggregating[Vector[String]] you must supply an Equality[String], either implicitly or explicitly. The contain syntax uses this Equality[E] to determine containership. Thus if you want to change how containership is determined for an element type E, place an implicit Equality[E] in scope or use the explicitly DSL. Although the implicit parameter required for the contain syntax is of type Aggregating[L], implicit conversions are provided in the Aggregating companion object from Equality[E] to the various types of aggregations of E. Here's an example:

The "contain inOrderOnly" syntax lets you assert that the containing object contains only the specified objects, in order. The specified objects may appear multiple times, but must appear in the order they appear in the right-hand list. Here's an example:

List(1, 2, 2, 3, 3, 3) must contain inOrderOnly (1, 2, 3)

The "contain inOrder" syntax lets you assert that the containing object contains only the specified objects in order, like inOrderOnly, but allows other objects to appear in the left-hand aggregation as well: contain more than one of each:

List(0, 1, 2, 2, 99, 3, 3, 3, 5) must contain inOrder (1, 2, 3)

If you have a collection of elements that you'd like to use in a "in order" comparison, you can use "inOrderElementsOf," like this:

List(0, 1, 2, 2, 99, 3, 3, 3, 5) must contain inOrderElementsOf Array(1, 2, 3)

Note that "order" in inOrder, inOrderOnly, and theSameElementsInOrderAs (described below) in the Aggregation[L] instances built-in to ScalaTest is defined as "iteration order".

Lastly, the "contain theSameElementsInOrderAs" syntax lets you assert that two aggregations contain the same exact elements in the same (iteration) order:

List(1, 2, 3) must contain theSameElementsInOrderAs collection.mutable.TreeSet(3, 2, 1)

The previous assertion succeeds because the iteration order of aTreeSet is the natural ordering of its elements, which in this case is 1, 2, 3. An iterator obtained from the left-hand List will produce the same elements in the same order.

Note that no inOrderOnlyElementsOf matcher is provided, because it would have the same behavior as theSameElementsInOrderAs. (I.e., if you were looking for inOrderOnlyElementsOf, please use theSameElementsInOrderAs instead.)

Working with "sortables"

You can also ask whether the elements of "sortable" objects (such as Arrays, Java Lists, and GenSeqs) are in sorted order, like this:

List(1, 2, 3) mustBe sorted

Working with iterators

Although it seems desirable to provide similar matcher syntax for Scala and Java iterators to that provided for sequences like Seqs, Array, and java.util.List, the ephemeral nature of iterators makes this problematic. Some syntax (such as must contain) is relatively straightforward to support on iterators, but other syntax (such as, for example, Inspector expressions on nested iterators) is not. Rather than allowing inconsistencies between sequences and iterators in the API, we chose to not support any such syntax directly on iterators:

scala> val it = List(1, 2, 3).iterator
it: Iterator[Int] = non-empty iterator

scala> it must contain (2)
<console>:15: error: could not find implicit value for parameter typeClass1: org.scalatest.enablers.Containing[Iterator[Int]]
           it must contain (2)
              ^

Instead, you will need to convert your iterators to a sequence explicitly before using them in matcher expressions:

scala> it.toStream must contain (2)

We recommend you convert (Scala or Java) iterators to Streams, as shown in the previous example, so that you can continue to reap any potential benefits provided by the laziness of the underlying iterator.

Inspector shorthands

You can use the Inspectors syntax with matchers as well as assertions. If you have a multi-dimensional collection, such as a list of lists, using Inspectors is your best option:

val yss =
  List(
    List(1, 2, 3),
    List(1, 2, 3),
    List(1, 2, 3)
  )

forAll (yss) { ys =>
  forAll (ys) { y => y must be > 0 }
}

For assertions on one-dimensional collections, however, matchers provides "inspector shorthands." Instead of writing:

val xs = List(1, 2, 3)
forAll (xs) { x => x must be < 10 }

You can write:

all (xs) must be < 10

The previous statement asserts that all elements of the xs list must be less than 10. All of the inspectors have shorthands in matchers. Here is the full list:

all - succeeds if the assertion holds true for every element
atLeast - succeeds if the assertion holds true for at least the specified number of elements
atMost - succeeds if the assertion holds true for at most the specified number of elements
between - succeeds if the assertion holds true for between the specified minimum and maximum number of elements, inclusive
every - same as all, but lists all failing elements if it fails (whereas all just reports the first failing element)
exactly - succeeds if the assertion holds true for exactly the specified number of elements

Here are some examples:

scala> import org.scalatest.MustMatchers._
import org.scalatest.MustMatchers._

scala> val xs = List(1, 2, 3, 4, 5)
xs: List[Int] = List(1, 2, 3, 4, 5)

scala> all (xs) must be > 0

scala> atMost (2, xs) must be >= 4

scala> atLeast (3, xs) must be < 5

scala> between (2, 3, xs) must (be > 1 and be < 5)

scala> exactly (2, xs) must be <= 2

scala> every (xs) must be < 10

scala> // And one that fails...

scala> exactly (2, xs) mustEqual 2
org.scalatest.exceptions.TestFailedException: 'exactly(2)' inspection failed, because only 1 element
    satisfied the assertion block at index 1:
  at index 0, 1 did not equal 2,
  at index 2, 3 did not equal 2,
  at index 3, 4 did not equal 2,
  at index 4, 5 did not equal 2
in List(1, 2, 3, 4, 5)
        at ...

Like Inspectors, objects used with inspector shorthands can be any type T for which a Collecting[T, E] is available, which by default includes GenTraversable, Java Collection, Java Map, Arrays, and Strings. Here are some examples:

scala> import org.scalatest._
import org.scalatest._

scala> import MustMatchers._
import MustMatchers._

scala> all (Array(1, 2, 3)) must be < 5

scala> import collection.JavaConverters._
import collection.JavaConverters._

scala> val js = List(1, 2, 3).asJava
js: java.util.List[Int] = [1, 2, 3]

scala> all (js) must be < 5

scala> val jmap = Map("a" -> 1, "b" -> 2).asJava
jmap: java.util.Map[String,Int] = {a=1, b=2}

scala> atLeast(1, jmap) mustBe Entry("b", 2)

scala> atLeast(2, "hello, world!") mustBe 'o'

Single-element collections

To assert both that a collection contains just one "lone" element as well as something else about that element, you can use the loneElement syntax provided by trait LoneElement. For example, if a Set[Int] must contain just one element, an Int less than or equal to 10, you could write:

import LoneElement._
set.loneElement must be <= 10

You can invoke loneElement on any type T for which an implicit Collecting[E, T] is available, where E is the element type returned by the loneElement invocation. By default, you can use loneElement on GenTraversable, Java Collection, Java Map, Array, and String.

Java collections and maps

You can use similar syntax on Java collections (java.util.Collection) and maps (java.util.Map). For example, you can check whether a Java Collection or Map is empty, like this:

javaCollection must be ('empty)
javaMap must be ('empty)

Even though Java's List type doesn't actually have a length or getLength method, you can nevertheless check the length of a Java List (java.util.List) like this:

javaList must have length 9

You can check the size of any Java Collection or Map, like this:

javaMap must have size 20
javaSet must have size 90

In addition, you can check whether a Java Collection contains a particular element, like this:

javaCollection must contain ("five")

One difference to note between the syntax supported on Java and Scala collections is that in Java, Map is not a subtype of Collection, and does not actually define an element type. You can ask a Java Map for an "entry set" via the entrySet method, which will return the Map's key/value pairs wrapped in a set of java.util.Map.Entry, but a Map is not actually a collection of Entry. To make Java Maps easier to work with, however, ScalaTest matchers allows you to treat a Java Map as a collection of Entry, and defines a convenience implementation of java.util.Map.Entry in org.scalatest.Entry. Here's how you use it:

javaMap must contain (Entry(2, 3))
javaMap must contain oneOf (Entry(2, 3), Entry(3, 4))

You can also just check whether a Java Map contains a particular key, or value, like this:

javaMap must contain key 1
javaMap must contain value "Howdy"

`String`s and `Array`s as collections

You can also use all the syntax described above for Scala and Java collections on Arrays and Strings. Here are some examples:

scala> import org.scalatest._
import org.scalatest._

scala> import MustMatchers._
import MustMatchers._

scala> atLeast (2, Array(1, 2, 3)) must be > 1

scala> atMost (2, "halloo") mustBe 'o'

scala> Array(1, 2, 3) mustBe sorted

scala> "abcdefg" mustBe sorted

scala> Array(1, 2, 3) must contain atMostOneOf (3, 4, 5)

scala> "abc" must contain atMostOneOf ('c', 'd', 'e')

`be` as an equality comparison

All uses of be other than those shown previously perform an equality comparison. They work the same as equal when it is used with default equality. This redundancy between be and equals exists in part because it enables syntax that sometimes sounds more natural. For example, instead of writing:

result must equal (null)

You can write:

result must be (null)

(Hopefully you won't write that too much given null is error prone, and Option is usually a better, well, option.) As mentioned previously, the other difference between equal and be is that equal delegates the equality check to an Equality typeclass, whereas be always uses default equality. Here are some other examples of be used for equality comparison:

sum must be (7.0)
boring must be (false)
fun must be (true)
list must be (Nil)
option must be (None)
option must be (Some(1))

As with equal used with default equality, using be on arrays results in deep being called on both arrays prior to calling equal. As a result, the following expression would not throw a TestFailedException:

Array(1, 2) must be (Array(1, 2)) // succeeds (i.e., does not throw TestFailedException)

Because be is used in several ways in ScalaTest matcher syntax, just as it is used in many ways in English, one potential point of confusion in the event of a failure is determining whether be was being used as an equality comparison or in some other way, such as a property assertion. To make it more obvious when be is being used for equality, the failure messages generated for those equality checks will include the word equal in them. For example, if this expression fails with a TestFailedException:

option must be (Some(1))

The detail message in that TestFailedException will include the words "equal to" to signify be was in this case being used for equality comparison:

Some(2) was not equal to Some(1)

Being negative

If you wish to check the opposite of some condition, you can simply insert not in the expression. Here are a few examples:

result must not be (null)
sum must not be <= (10)
mylist must not equal (yourList)
string must not startWith ("Hello")

Checking that a snippet of code does not compile

Often when creating libraries you may wish to ensure that certain arrangements of code that represent potential “user errors” do not compile, so that your library is more error resistant. ScalaTest Matchers trait includes the following syntax for that purpose:

"val a: String = 1" mustNot compile

If you want to ensure that a snippet of code does not compile because of a type error (as opposed to a syntax error), use:

"val a: String = 1" mustNot typeCheck

Note that the mustNot typeCheck syntax will only succeed if the given snippet of code does not compile because of a type error. A syntax error will still result in a thrown TestFailedException.

If you want to state that a snippet of code does compile, you can make that more obvious with:

"val a: Int = 1" must compile

Although the previous three constructs are implemented with macros that determine at compile time whether the snippet of code represented by the string does or does not compile, errors are reported as test failures at runtime.

Logical expressions with `and` and `or`

You can also combine matcher expressions with and and/or or, however, you must place parentheses or curly braces around the and or or expression. For example, this and-expression would not compile, because the parentheses are missing:

map must contain key ("two") and not contain value (7) // ERROR, parentheses missing!

Instead, you need to write:

map must (contain key ("two") and not contain value (7))

Here are some more examples:

number must (be > (0) and be <= (10))
option must (equal (Some(List(1, 2, 3))) or be (None))
string must (
  equal ("fee") or
  equal ("fie") or
  equal ("foe") or
  equal ("fum")
)

Two differences exist between expressions composed of these and and or operators and the expressions you can write on regular Booleans using its && and || operators. First, expressions with and and or do not short-circuit. The following contrived expression, for example, would print "hello, world!":

"yellow" must (equal ("blue") and equal { println("hello, world!"); "green" })

In other words, the entire and or or expression is always evaluated, so you'll see any side effects of the right-hand side even if evaluating only the left-hand side is enough to determine the ultimate result of the larger expression. Failure messages produced by these expressions will "short-circuit," however, mentioning only the left-hand side if that's enough to determine the result of the entire expression. This "short-circuiting" behavior of failure messages is intended to make it easier and quicker for you to ascertain which part of the expression caused the failure. The failure message for the previous expression, for example, would be:

"yellow" did not equal "blue"

Most likely this lack of short-circuiting would rarely be noticeable, because evaluating the right hand side will usually not involve a side effect. One situation where it might show up, however, is if you attempt to and a null check on a variable with an expression that uses the variable, like this:

map must (not be (null) and contain key ("ouch"))

If map is null, the test will indeed fail, but with a NullArgumentException, not a TestFailedException. Here, the NullArgumentException is the visible right-hand side effect. To get a TestFailedException, you would need to check each assertion separately:

map must not be (null)
map must contain key ("ouch")

If map is null in this case, the null check in the first expression will fail with a TestFailedException, and the second expression will never be executed.

The other difference with Boolean operators is that although && has a higher precedence than ||, and and or have the same precedence. Thus although the Boolean expression (a || b && c) will evaluate the && expression before the || expression, like (a || (b && c)), the following expression:

traversable must (contain (7) or contain (8) and have size (9))

Will evaluate left to right, as:

traversable must ((contain (7) or contain (8)) and have size (9))

If you really want the and part to be evaluated first, you'll need to put in parentheses, like this:

traversable must (contain (7) or (contain (8) and have size (9)))

Working with `Option`s

You can work with options using ScalaTest's equality, empty, defined, and contain syntax. For example, if you wish to check whether an option is None, you can write any of:

option mustEqual None
option mustBe None
option must === (None)
option mustBe empty

If you wish to check an option is defined, and holds a specific value, you can write any of:

option mustEqual Some("hi")
option mustBe Some("hi")
option must === (Some("hi"))

If you only wish to check that an option is defined, but don't care what it's value is, you can write:

option mustBe defined

If you mix in (or import the members of) OptionValues, you can write one statement that indicates you believe an option must be defined and then say something else about its value. Here's an example:

import org.scalatest.OptionValues._
option.value must be < 7

As mentioned previously, you can use also use ScalaTest's contain, contain oneOf, and contain noneOf syntax with options:

Some(2) must contain (2)
Some(7) must contain oneOf (5, 7, 9)
Some(0) must contain noneOf (7, 8, 9)

Checking arbitrary properties with `have`

Using have, you can check properties of any type, where a property is an attribute of any object that can be retrieved either by a public field, method, or JavaBean-style get or is method, like this:

book must have (
  'title ("Programming in Scala"),
  'author (List("Odersky", "Spoon", "Venners")),
  'pubYear (2008)
)

This expression will use reflection to ensure the title, author, and pubYear properties of object book are equal to the specified values. For example, it will ensure that book has either a public Java field or method named title, or a public method named getTitle, that when invoked (or accessed in the field case) results in the string "Programming in Scala". If all specified properties exist and have their expected values, respectively, execution will continue. If one or more of the properties either does not exist, or exists but results in an unexpected value, a TestFailedException will be thrown that explains the problem. (For the details on how a field or method is selected during this process, see the documentation for HavePropertyMatcherGenerator.)

When you use this syntax, you must place one or more property values in parentheses after have, separated by commas, where a property value is a symbol indicating the name of the property followed by the expected value in parentheses. The only exceptions to this rule is the syntax for checking size and length shown previously, which does not require parentheses. If you forget and put parentheses in, however, everything will still work as you'd expect. Thus instead of writing:

array must have length (3)
set must have size (90)

You can alternatively, write:

array must have (length (3))
set must have (size (90))

If a property has a value different from the specified expected value, a TestFailedError will be thrown with a detailed message that explains the problem. For example, if you assert the following on a book whose title is Moby Dick:

book must have ('title ("A Tale of Two Cities"))

You'll get a TestFailedException with this detail message:

The title property had value "Moby Dick", instead of its expected value "A Tale of Two Cities",
on object Book("Moby Dick", "Melville", 1851)

If you prefer to check properties in a type-safe manner, you can use a HavePropertyMatcher. This would allow you to write expressions such as:

book must have (
  title ("Programming in Scala"),
  author (List("Odersky", "Spoon", "Venners")),
  pubYear (2008)
)

These expressions would fail to compile if must is used on an inappropriate type, as determined by the type parameter of the HavePropertyMatcher being used. (For example, title in this example might be of type HavePropertyMatcher[org.publiclibrary.Book]. If used with an appropriate type, such an expression will compile and at run time the property method or field will be accessed directly; i.e., no reflection will be used. See the documentation for HavePropertyMatcher for more information.

Using `length` and `size` with `HavePropertyMatcher`s

If you want to use length or size syntax with your own custom HavePropertyMatchers, you can do so, but you must write (of [“the type”]) afterwords. For example, you could write:

book must have (
  title ("A Tale of Two Cities"),
  length (220) (of [Book]),
  author ("Dickens")
)

Prior to ScalaTest 2.0, “length (22)” yielded a HavePropertyMatcher[Any, Int] that used reflection to dynamically look for a length field or getLength method. In ScalaTest 2.0, “length (22)” yields a MatcherFactory1[Any, Length], so it is no longer a HavePropertyMatcher. The (of [<type>]) syntax converts the the MatcherFactory1[Any, Length] to a HavePropertyMatcher[<type>, Int].

Checking that an expression matches a pattern

ScalaTest's Inside trait allows you to make assertions after a pattern match. Here's an example:

case class Name(first: String, middle: String, last: String)

val name = Name("Jane", "Q", "Programmer")

inside(name) { case Name(first, _, _) =>
  first must startWith ("S")
}

You can use inside to just ensure a pattern is matched, without making any further assertions, but a better alternative for that kind of assertion is matchPattern. The matchPattern syntax allows you to express that you expect a value to match a particular pattern, no more and no less:

name must matchPattern { case Name("Sarah", _, _) => }

Using custom matchers

If none of the built-in matcher syntax (or options shown so far for extending the syntax) satisfy a particular need you have, you can create custom Matchers that allow you to place your own syntax directly after must. For example, class java.io.File has a method isHidden, which indicates whether a file of a certain path and name is hidden. Because the isHidden method takes no parameters and returns Boolean, you can call it using be with a symbol or BePropertyMatcher, yielding assertions like:

file must be ('hidden)  // using a symbol
file must be (hidden)   // using a BePropertyMatcher

If it doesn't make sense to have your custom syntax follow be, you might want to create a custom Matcher instead, so your syntax can follow must directly. For example, you might want to be able to check whether a java.io.File's name ends with a particular extension, like this:

// using a plain-old Matcher
file must endWithExtension ("txt")

ScalaTest provides several mechanism to make it easy to create custom matchers, including ways to compose new matchers out of existing ones complete with new error messages. For more information about how to create custom Matchers, please see the documentation for the Matcher trait.

Checking for expected exceptions

Sometimes you need to test whether a method throws an expected exception under certain circumstances, such as when invalid arguments are passed to the method. With Matchers mixed in, you can check for an expected exception like this:

an [IndexOutOfBoundsException] must be thrownBy s.charAt(-1)

If charAt throws an instance of StringIndexOutOfBoundsException, this expression will result in that exception. But if charAt completes normally, or throws a different exception, this expression will complete abruptly with a TestFailedException.

If you need to further inspect an expected exception, you can capture it using this syntax:

val thrown = the [IndexOutOfBoundsException] thrownBy s.charAt(-1)

This expression returns the caught exception so that you can inspect it further if you wish, for example, to ensure that data contained inside the exception has the expected values. Here's an example:

thrown.getMessage must equal ("String index out of range: -1")

If you prefer you can also capture and inspect an expected exception in one statement, like this:

the [ArithmeticException] thrownBy 1 / 0 must have message "/ by zero"
the [IndexOutOfBoundsException] thrownBy {
  s.charAt(-1)
} must have message "String index out of range: -1"

You can also state that no exception must be thrown by some code, like this:

noException must be thrownBy 0 / 1

Those pesky parens

Perhaps the most tricky part of writing assertions using ScalaTest matchers is remembering when you need or don't need parentheses, but bearing in mind a few simple rules should help. It is also reassuring to know that if you ever leave off a set of parentheses when they are required, your code will not compile. Thus the compiler will help you remember when you need the parens. That said, the rules are:

1. Although you don't always need them, you may choose to always put parentheses around right-hand values, such as the 7 in num must equal (7):

result must equal (4)
array must have length (3)
book must have (
  'title ("Programming in Scala"),
  'author (List("Odersky", "Spoon", "Venners")),
  'pubYear (2008)
)
option must be ('defined)
catMap must (contain key (9) and contain value ("lives"))
keyEvent must be an ('actionKey)
javaSet must have size (90)

2. Except for length, size and message, you must always put parentheses around the list of one or more property values following a have:

file must (exist and have ('name ("temp.txt")))
book must have (
  title ("Programming in Scala"),
  author (List("Odersky", "Spoon", "Venners")),
  pubYear (2008)
)
javaList must have length (9) // parens optional for length and size

3. You must always put parentheses around and and or expressions, as in:

catMap must (contain key (9) and contain value ("lives"))
number must (equal (2) or equal (4) or equal (8))

4. Although you don't always need them, you may choose to always put parentheses around custom Matchers when they appear directly after not:

file must exist
file must not (exist)
file must (exist and have ('name ("temp.txt")))
file must (not (exist) and have ('name ("temp.txt"))
file must (have ('name ("temp.txt") or exist)
file must (have ('name ("temp.txt") or not (exist))

That's it. With a bit of practice it should become natural to you, and the compiler will always be there to tell you if you forget a set of needed parentheses.

Note: ScalaTest's matchers are in part inspired by the matchers of RSpec, Hamcrest, and specs2, and its “mustNot compile” syntax by the illTyped macro of shapeless.

trait NonImplicitAssertions extends Assertions

Trait that can be mixed into a Suite to disable the implicit conversions provided by default in trait Assertions, which trait Suite extends.

This trait can be used to quickly solve a problem in which ScalaTest's default implicit conversion is clashing with those of some other library you need to use in your tests. After mixing in this trait, like this:

class MySuite extends FunSuite with NonImplicitAssertions {
  // ... 
}

You can write tests using assert (without triple equals), assertResult, assertThrows, intercept, assertCompiles, assertDoesNotCompile, and assertTypeError:

assert(a < 7)

assertResult(2) { 1 + 1 }

assertThrows[IndexOutOfBoundsException] {
  "hi".charAt(-1)
}

val caught =
  intercept[IndexOutOfBoundsException] {
    "hi".charAt(-1)
  }

assertDoesNotCompile("val a: String = 1")

assertTypeError("val a: String = 1")

assertCompiles("val a: Int = 1")

trait Notifier extends AnyRef

Trait providing an apply method to which status updates about a running suite of tests can be reported.

An Notifier is essentially used to wrap a Reporter and provide easy ways to send status updates to that Reporter via an NoteProvided event. Notifier contains an apply method that takes a string and an optional payload object of type Any. The Notifier will forward the passed alert message string to the Reporter as the message parameter, and the optional payload object as the payload parameter, of an NoteProvided event.

For insight into the differences between Notifier, Alerter, and Informer, see the main documentation for trait Notifying.

trait Notifying extends AnyRef

Trait that contains the note method, which can be used to send a status notification to the reporter.

The difference between note and the info method of Informer is that info messages provided during a test are recorded and sent as part of test completion event, whereas note messages are sent right away as NoteProvided messages. For long-running tests, note allows you to send "status notifications" to the reporter right away, so users can track the progress of the long-running tests. By contrast, info messages will only be seen by the user after the test has completed, and are more geared towards specification (such as Given/When/Then messages) than notification.

The difference between note and the alert method of Alerting is that alert is intended to be used for warnings or notifications of potential problems, whereas note is just for status notifications. In string reporters for which ANSI color is enabled, note notifications are shown in green and alert notifications in yellow.

trait OneInstancePerTest extends SuiteMixin

Trait that facilitates a style of testing in which each test is run in its own instance of the suite class to isolate each test from the side effects of the other tests in the suite.

Recommended Usage: Trait OneInstancePerTest is intended primarily to serve as a supertrait for ParallelTestExecution and the path traits, to facilitate porting JUnit tests to ScalaTest, and to make it easy for users who prefer JUnit's approach to isolation to obtain similar behavior in ScalaTest.

If you mix this trait into a Suite, you can initialize shared reassignable fixture variables as well as shared mutable fixture objects in the constructor of the class. Because each test will run in its own instance of the class, each test will get a fresh copy of the instance variables. This is the approach to test isolation taken, for example, by the JUnit framework. OneInstancePerTest can, therefore, be handy when porting JUnit tests to ScalaTest.

Here's an example of OneInstancePerTest being used in a FunSuite:

import org.scalatest.FunSuite
import org.scalatest.OneInstancePerTest
import collection.mutable.ListBuffer

class MySuite extends FunSuite with OneInstancePerTest {

  val builder = new StringBuilder("ScalaTest is ")
  val buffer = new ListBuffer[String]

  test("easy") {
    builder.append("easy!")
    assert(builder.toString === "ScalaTest is easy!")
    assert(buffer.isEmpty)
    buffer += "sweet"
  }

  test("fun") {
    builder.append("fun!")
    assert(builder.toString === "ScalaTest is fun!")
    assert(buffer.isEmpty)
  }
}

OneInstancePerTest is supertrait to ParallelTestExecution, in which running each test in its own instance is intended to make it easier to write suites of tests that run in parallel (by reducing the likelihood of concurrency bugs in those suites.) OneInstancePerTest is also supertrait to the path traits, path.FunSpec and path.FreeSpec, to make it obvious these traits run each test in a new, isolated instance.

For the details on how OneInstancePerTest works, see the documentation for methods runTests and runTest, which this trait overrides.

trait OptionValues extends AnyRef

Trait that provides an implicit conversion that adds a value method to Option, which will return the value of the option if it is defined, or throw TestFailedException if not.

This construct allows you to express in one statement that an option should be defined and that its value should meet some expectation. Here's an example:

opt.value should be > 9

Or, using an assertion instead of a matcher expression:

assert(opt.value > 9)

Were you to simply invoke get on the Option, if the option wasn't defined, it would throw a NoSuchElementException:

val opt: Option[Int] = None

opt.get should be > 9 // opt.get throws NoSuchElementException

The NoSuchElementException would cause the test to fail, but without providing a stack depth pointing to the failing line of test code. This stack depth, provided by TestFailedException (and a few other ScalaTest exceptions), makes it quicker for users to navigate to the cause of the failure. Without OptionValues, to get a stack depth exception you would need to make two statements, like this:

val opt: Option[Int] = None

opt should be ('defined) // throws TestFailedException
opt.get should be > 9

The OptionValues trait allows you to state that more concisely:

val opt: Option[Int] = None

opt.value should be > 9 // opt.value throws TestFailedException

sealed abstract class Outcome extends Product with Serializable

Superclass for the possible outcomes of running a test.

Outcome is the result type of the withFixture methods of traits Suite and fixture.Suite, as well as their NoArgTest and OneArgTest function types. The four possible outcomes are:

Succeeded - indicates a test succeeded
Failed - indicates a test failed and contains an exception describing the failure
Canceled - indicates a test was canceled and contains an exception describing the cancelation
Pending - indicates a test was pending

Note that "ignored" does not appear as a type of Outcome, because tests are marked as ignored on the outside and skipped over as the suite executes. So an ignored test never runs, and therefore never has an outcome. By contrast, a test is determined to be pending by running the test and observing the actual outcome. If the test body completes abruptly with a TestPendingException, then the outcome was that the test was pending.

trait OutcomeOf extends AnyRef

Trait that contains the outcomeOf method, which executes a passed code block and transforms the outcome into an Outcome, using the same mechanism used by ScalaTest to produce an Outcome when executing a test.

For an example of outcomeOf in action, see the documentation for class TableFor2.

trait ParallelTestExecution extends OneInstancePerTest

Trait that causes that the tests of any suite it is mixed into to be run in parallel if a Distributor is passed to runTests.

ScalaTest's normal approach for running suites of tests in parallel is to run different suites in parallel, but the tests of any one suite sequentially. This approach should provide sufficient distribution of the work load in most cases, but some suites may encapsulate multiple long-running tests. Such suites may dominate the execution time of the run. If so, mixing in this trait into just those suites will allow their long-running tests to run in parallel with each other, thereby helping to reduce the total time required to run an entire run.

To make it easier for users to write tests that run in parallel, this trait runs each test in its own instance of the class. Running each test in its own instance enables tests to use the same instance vars and mutable objects referenced from instance variables without needing to synchronize. Although ScalaTest provides functional approaches to factoring out common test code that can help avoid such issues, running each test in its own instance is an insurance policy that makes running tests in parallel easier and less error prone.

For the details on how ParallelTestExecution works, see the documentation for methods run, runTests, and runTest, which this trait overrides.

Note: This trait's implementation of runTest is final, to ensure that behavior related to individual tests are executed by the same thread that executes the actual test. This means, for example, that you won't be allowed to write ...with ParallelTestExecution with BeforeAndAfter. Instead, you'd need to put ParallelTestExecution last, as in: with BeforeAndAfter with ParallelTestExecution. For more details, see the documentation for the runTest method.

trait PartialFunctionValues extends AnyRef

Trait that provides an implicit conversion that adds a valueAt method to PartialFunction, which will return the value (result) of the function applied to the argument passed to valueAt, or throw TestFailedException if the partial function is not defined at the argument.

This construct allows you to express in one statement that a partial function should be defined for a particular input, and that its result value should meet some expectation. Here's an example:

pf.valueAt("IV") should equal (4)

Or, using an assertion instead of a matcher expression:

assert(pf.valueAt("IV") === 4)

Were you to simply invoke apply on the PartialFunction, passing in an input value, if the partial function wasn't defined at that input, it would throw some exception, but likely not one that provides a stack depth:

// Note: a Map[K, V] is a PartialFunction[K, V]
val pf: PartialFunction[String, Int] = Map("I" -> 1, "II" -> 2, "III" -> 3, "IV" -> 4)

pf("V") should equal (5) // pf("V") throws NoSuchElementException

The NoSuchElementException thrown in this situation would cause the test to fail, but without providing a stack depth pointing to the failing line of test code. This stack depth, provided by TestFailedException (and a few other ScalaTest exceptions), makes it quicker for users to navigate to the cause of the failure. Without PartialFunctionValues, to get a stack depth exception you would need to make two statements, like this:

val pf: PartialFunction[String, Int] = Map("I" -> 1, "II" -> 2, "III" -> 3, "IV" -> 4)

pf.isDefinedAt("V") should be (true) // throws TestFailedException
pf("V") should equal (5)

The PartialFunctionValues trait allows you to state that more concisely:

val pf: PartialFunction[String, Int] = Map("I" -> 1, "II" -> 2, "III" -> 3, "IV" -> 4)

pf.valueAt("V") should equal (5) // pf.valueAt("V") throws TestFailedException

trait Payloads extends AnyRef

Trait facilitating the inclusion of a payload in a thrown ScalaTest exception.

This trait includes a withPayload construct that enables a payload object (or modified payload object) to be included as the payload of a thrown exception.

Many ScalaTest events include an optional "payload" field that can be used to pass information to a custom reporter. This trait facilitates such customization, by making it easy to insert a payload into a thrown exception, such as a TestFailedException. The thrown exception must mix in Payload. ScalaTest looks for trait Payload and fires any payloads it finds in the relevant ScalaTest event stimulated by the exception, such as a TestFailed event stimulated by a TestFailedException. Here's an example in which a GUI snapshot is included as a payload when a test fails:

withPayload(generateGUISnapshot()) {
  1 + 1 should === (3)
}

sealed trait PendingStatement extends AnyRef

Trait mixed into the result type of the pending statement of trait Assertions, which always throws TestPendingException.

This type is used primarily to facilitate the is (pending) syntax of traits FlatSpec, WordSpec, and FLatSpec as well the is (pending) or (pending) syntax of sibling traits in the org.scalatest.fixture package. Because the pending method in Assertions always completes abruptly with an exception, its type would be inferred to be Nothing, which is a relatively common type. To make sure syntax like is (pending) only works with method pending, it is helpful to have a specially named "Nothing" type.

trait PrivateMethodTester extends AnyRef

Trait that facilitates the testing of private methods.

To test a private method, mix in trait PrivateMethodTester and create a PrivateMethod object, like this:

val decorateToStringValue = PrivateMethod[String]('decorateToStringValue)

The type parameter on PrivateMethod, in this case String, is the result type of the private method you wish to invoke. The symbol passed to the PrivateMethod.apply factory method, in this case 'decorateToStringValue, is the name of the private method to invoke. To test the private method, use the invokePrivate operator, like this:

targetObject invokePrivate decorateToStringValue(1)

Here, targetObject is a variable or singleton object name referring to the object whose private method you want to test. You pass the arguments to the private method in the parentheses after the PrivateMethod object. The result type of an invokePrivate operation will be the type parameter of the PrivateMethod object, thus you need not cast the result to use it. In other words, after creating a PrivateMethod object, the syntax to invoke the private method looks like a regular method invocation, but with the dot (.) replaced by invokePrivate. The private method is invoked dynamically via reflection, so if you have a typo in the method name symbol, specify the wrong result type, or pass invalid parameters, the invokePrivate operation will compile, but throw an exception at runtime.

One limitation to be aware of is that you can't use PrivateMethodTester to test a private method declared in a trait, because the class the trait gets mixed into will not declare that private method. Only the class generated to hold method implementations for the trait will have that private method. If you want to test a private method declared in a trait, and that method does not use any state of that trait, you can move the private method to a companion object for the trait and test it using PrivateMethodTester that way. If the private trait method you want to test uses the trait's state, your best options are to test it indirectly via a non-private trait method that calls the private method, or make the private method package access and test it directly via regular static method invocations.

Also, if you want to use PrivateMethodTester to invoke a parameterless private method, you'll need to use empty parens. Instead of:

targetObject invokePrivate privateParameterlessMethod

You'll need to write:

targetObject invokePrivate privateParameterlessMethod()

class PropSpec extends PropSpecLike

A suite of property-based tests.

Recommended Usage: Class PropSpec is a good fit for teams that want to write tests exclusively in terms of property checks, and is also a good choice for writing the occasional test matrix when a different style trait is chosen as the main unit testing style.

Here's an example PropSpec:

package org.scalatest.examples.propspec

import org.scalatest._
import prop._
import scala.collection.immutable._

class SetSpec extends PropSpec with TableDrivenPropertyChecks with Matchers {

  val examples =
    Table(
      "set",
      BitSet.empty,
      HashSet.empty[Int],
      TreeSet.empty[Int]
    )

  property("an empty Set should have size 0") {
    forAll(examples) { set =>
      set.size should be (0)
    }
  }

  property("invoking head on an empty set should produce NoSuchElementException") {
    forAll(examples) { set =>
      a [NoSuchElementException] should be thrownBy { set.head }
    }
  }
}

You can run a PropSpec by invoking execute on it. This method, which prints test results to the standard output, is intended to serve as a convenient way to run tests from within the Scala interpreter. For example, to run SetSpec from within the Scala interpreter, you could write:

scala> org.scalatest.run(new SetSpec)

And you would see:

SetSpec:
- an empty Set should have size 0
- invoking head on an empty Set should produce NoSuchElementException

Or, to run just the “an empty Set should have size 0” method, you could pass that test's name, or any unique substring of the name, such as "size 0" or even just "0". Here's an example:

scala> org.scalatest.run(new SetSpec, "size 0")
SetSpec:
- an empty Set should have size 0

You can also pass to execute a config map of key-value pairs, which will be passed down into suites and tests, as well as other parameters that configure the run itself. For more information on running in the Scala interpreter, see the documentation for execute (below) and the ScalaTest shell.

The execute method invokes a run method that takes two parameters. This run method, which actually executes the suite, will usually be invoked by a test runner, such as run, tools.Runner, a build tool, or an IDE.

“property” is a method, defined in PropSpec, which will be invoked by the primary constructor of SetSpec. You specify the name of the test as a string between the parentheses, and the test code itself between curly braces. The test code is a function passed as a by-name parameter to property, which registers it for later execution.

A PropSpec's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Tests can only be registered with the property method while the PropSpec is in its registration phase. Any attempt to register a test after the PropSpec has entered its ready phase, i.e., after run has been invoked on the PropSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using PropSpec is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, PropSpec provides registration methods that start with ignore instead of property. Here's an example:

package org.scalatest.examples.suite.ignore

import org.scalatest._
import prop._
import scala.collection.immutable._

class SetSpec extends PropSpec with TableDrivenPropertyChecks with Matchers {

  val examples =
    Table(
      "set",
      BitSet.empty,
      HashSet.empty[Int],
      TreeSet.empty[Int]
    )

  ignore("an empty Set should have size 0") {
    forAll(examples) { set =>
      set.size should be (0)
    }
  }

  property("invoking head on an empty set should produce NoSuchElementException") {
    forAll(examples) { set =>
      a [NoSuchElementException] should be thrownBy { set.head }
    }
  }
}

If you run this version of SetSuite with:

scala> org.scalatest.run(new SetSpec)

It will run only the second test and report that the first test was ignored:

SetSuite:
- an empty Set should have size 0 !!! IGNORED !!!
- invoking head on an empty Set should produce NoSuchElementException

Informers

One of the parameters to PropSpec's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the reporting done by default by PropSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event. Here's an example that shows both a direct use as well as an indirect use through the methods of GivenWhenThen:

package org.scalatest.examples.propspec.info

import org.scalatest._
import prop._
import collection.mutable

class SetSpec extends PropSpec with TableDrivenPropertyChecks with GivenWhenThen {

  val examples =
    Table(
      "set",
      mutable.BitSet.empty,
      mutable.HashSet.empty[Int],
      mutable.LinkedHashSet.empty[Int]
    )

  property("an element can be added to an empty mutable Set") {

    forAll(examples) { set =>

      info("—————-")

      Given("an empty mutable " + set.getClass.getSimpleName)
      assert(set.isEmpty)

      When("an element is added")
      set += 99

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains(99))
    }
  }
}

If you run this PropSpec from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSpec)
SetSpec:
- an element can be added to an empty mutable Set
  + ----------------
  + Given an empty mutable BitSet
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + ----------------
  + Given an empty mutable HashSet
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + ----------------
  + Given an empty mutable LinkedHashSet
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element

Documenters

PropSpec also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example PropSpec that uses markup:

package org.scalatest.examples.propspec.markup

import org.scalatest._
import prop._
import collection.mutable

class SetSpec extends PropSpec with TableDrivenPropertyChecks with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

    def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  val examples =
    Table(
      "set",
      mutable.BitSet.empty,
      mutable.HashSet.empty[Int],
      mutable.LinkedHashSet.empty[Int]
    )

  property("an element can be added to an empty mutable Set") {

    forAll(examples) { set =>

      info("—————-")

      Given("an empty mutable " + set.getClass.getSimpleName)
      assert(set.isEmpty)

      When("an element is added")
      set += 99

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains(99))
    }

    markup("This test finished with a **bold** statement!")
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.propspec.note

import org.scalatest._
import prop._
import collection.mutable

class SetSpec extends PropSpec with TableDrivenPropertyChecks {

  val examples =
    Table(
      "set",
      mutable.BitSet.empty,
      mutable.HashSet.empty[Int],
      mutable.LinkedHashSet.empty[Int]
    )

  property("an element can be added to an empty mutable Set") {

    info("info is recorded")
    markup("markup is *also* recorded")
    note("notes are sent immediately")
    alert("alerts are also sent immediately")

    forAll(examples) { set =>

      assert(set.isEmpty)
      set += 99
      assert(set.size === 1)
      assert(set.contains(99))
    }
  }
}

Because note and alert information is sent immediately, it will appear before the test name in string reporters, and its color will be unrelated to the ultimate outcome of the test: note text will always appear in green, alert text will always appear in yellow. Here's an example:

scala> org.scalatest.run(new SetSpec)
SetSpec:
  + notes are sent immediately
  + alerts are also sent immediately
- an element can be added to an empty mutable Set
  + info is recorded
  + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. The test can also include some code that sends more information about the behavior to the reporter when the tests run. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (The code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality, has not yet been implemented.

You can mark tests pending in PropSpec like this:

import org.scalatest._
import prop._
import scala.collection.immutable._

class SetSpec extends PropSpec with TableDrivenPropertyChecks with Matchers {

  val examples =
    Table(
      "set",
      BitSet.empty,
      HashSet.empty[Int],
      TreeSet.empty[Int]
    )

  property("an empty Set should have size 0") (pending)

  property("invoking head on an empty set should produce NoSuchElementException") {
    forAll(examples) { set =>
      a [NoSuchElementException] should be thrownBy { set.head }
    }
  }
}

(Note: "(pending)" is the body of the test. Thus the test contains just one statement, an invocation of the pending method, which throws TestPendingException.) If you run this version of SetSuite with:

scala> org.scalatest.run(new SetSuite)

It will run both tests, but report that first test is pending. You'll see:

SetSuite:
- An empty Set should have size 0 (pending)
- Invoking head on an empty Set should produce NoSuchElementException

One difference between an ignored test and a pending one is that an ignored test is intended to be used during a significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException. The reason for this difference is that it enables your unfinished test to send InfoProvided messages to the reporter before it completes abruptly with TestPendingException, as shown in the previous example on Informers that used the GivenWhenThen trait.

Tagging tests

A PropSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing a PropSpec, groups of tests can optionally be included and/or excluded. To tag a PropSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified names, com.mycompany.tags.DbTest, then you could create a matching tag for PropSpecs like this:

package org.scalatest.examples.propspec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place PropSpec tests into groups with tags like this:

import org.scalatest._
import prop._
import tagobjects.Slow
import scala.collection.immutable._

class SetSpec extends PropSpec with TableDrivenPropertyChecks with Matchers {

  val examples =
    Table(
      "set",
      BitSet.empty,
      HashSet.empty[Int],
      TreeSet.empty[Int]
    )

  property("an empty Set should have size 0", Slow) {
    forAll(examples) { set =>
      set.size should be (0)
    }
  }

  property("invoking head on an empty set should produce NoSuchElementException",
      Slow, DbTest) {

    forAll(examples) { set =>
      a [NoSuchElementException] should be thrownBy { set.head }
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and more amenable for parallel test execution.

The techniques in PropSpec are identical to those in FunSuite, but with “test” replaced by “property”. The following table summarizes the options with a link to the relevant documentation for trait FunSuite:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
fixture-context objects	By placing fixture methods and fields into traits, you can easily give each test just the newly created fixtures it needs by mixing together traits. Use this technique when you need different combinations of mutable fixture objects in different tests, and don't need to clean up after.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgTest)` instead)
`withFixture(OneArgTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Using `PropSpec` to implement a test matrix

Using fixture-context objects in a PropSpec is a good way to implement a test matrix. What is the matrix? A test matrix is a series of tests that you need to run on a series of subjects. For example, The Scala API contains many implementations of trait Set. Every implementation must obey the contract of Set. One property of any Set is that an empty Set should have size 0, another is that invoking head on an empty Set should give you a NoSuchElementException, and so on. Already you have a matrix, where rows are the properties and the columns are the set implementations:

	`BitSet`	`HashSet`	`TreeSet`
An empty Set should have size 0	pass	pass	pass
Invoking head on an empty set should produce NoSuchElementException	pass	pass	pass

One way to implement this test matrix is to define a trait to represent the columns (in this case, BitSet, HashSet, and TreeSet) as elements in a single-dimensional Table. Each element in the Table represents one Set implementation. Because different properties may require different fixture instances for those implementations, you can define a trait to hold the examples, like this:

trait SetExamples extends Tables {

  def examples = Table("set", bitSet, hashSet, treeSet)

  def bitSet: BitSet
  def hashSet: HashSet[Int]
  def treeSet: TreeSet[Int]
}

Given this trait, you could provide empty sets in one implementation of SetExamples, and non-empty sets in another. Here's how you might provide empty set examples:

class EmptySetExamples extends SetExamples {
  def bitSet = BitSet.empty
  def hashSet = HashSet.empty[Int]
  def treeSet = TreeSet.empty[Int]
}

And here's how you might provide set examples with one item each:

class SetWithOneItemExamples extends SetExamples {
  def bitSet = BitSet(1)
  def hashSet = HashSet(1)
  def treeSet = TreeSet(1)
}

Armed with these example classes, you can define checks of properties that require empty or non-empty set fixtures by using instances of these classes as fixture-context objects. In other words, the columns of the test matrix are implemented as elements of a one-dimensional table of fixtures, the rows are implemented as property clauses of a PropSpec.

Here's a complete example that checks the two properties mentioned previously:

package org.scalatest.examples.propspec.matrix

import org.scalatest._
import org.scalatest.prop._
import scala.collection.immutable._

trait SetExamples extends Tables {

  def examples = Table("set", bitSet, hashSet, treeSet)

  def bitSet: BitSet
  def hashSet: HashSet[Int]
  def treeSet: TreeSet[Int]
}

class EmptySetExamples extends SetExamples {
  def bitSet = BitSet.empty
  def hashSet = HashSet.empty[Int]
  def treeSet = TreeSet.empty[Int]
}

class SetSpec extends PropSpec with TableDrivenPropertyChecks with Matchers {

  property("an empty Set should have size 0") {
    new EmptySetExamples {
      forAll(examples) { set =>
        set.size should be (0)
      }
    }
  }

  property("invoking head on an empty set should produce NoSuchElementException") {
    new EmptySetExamples {
      forAll(examples) { set =>
        a [NoSuchElementException] should be thrownBy { set.head }
      }
    }
  }
}

One benefit of this approach is that the compiler will help you when you need to add either a new row or column to the matrix. In either case, you'll need to ensure all cells are checked to get your code to compile.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. That is to say, you may want to write tests that are "shared" by different fixture objects. You accomplish this in a PropSpec in the same way you would do it in a FunSuite, except instead of test you say property, and instead of testsFor you say propertiesFor. For more information, see the Shared tests section of FunSuite's documentation.

trait PropSpecLike extends TestSuite with TestRegistration with Informing with Notifying with Alerting with Documenting

Implementation trait for class PropSpec, which represents a suite of property-based tests.

PropSpec is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of PropSpec into some other class, you can use this trait instead, because class PropSpec does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of PropSpec.

trait RandomTestOrder extends OneInstancePerTest

Trait that causes tests to be run in pseudo-random order.

Although the tests are run in pseudo-random order, events will be fired in the “normal” order for the Suite that mixes in this trait, as determined by runTests.

The purpose of this trait is to reduce the likelihood of unintentional order dependencies between tests in the same test class.

trait RecoverMethods extends AnyRef

Offers two methods for transforming futures when exceptions are expected.

This trait offers two methods for testing for expected exceptions in the context of futures: recoverToSucceededIf and recoverToExceptionIf. Because this trait is mixed into trait AsyncTestSuite, both of its methods are available by default in any async-style suite.

If you just want to ensure that a future fails with a particular exception type, and do not need to inspect the exception further, use recoverToSucceededIf:

recoverToSucceededIf[IllegalStateException] { // Result type: Future[Assertion]
  emptyStackActor ? Peek
}

The recoverToSucceededIf method performs a job similar to assertThrows, except in the context of a future. It transforms a Future of any type into a Future[Assertion] that succeeds only if the original future fails with the specified exception. Here's an example in the REPL:

scala> import org.scalatest.RecoverMethods._
import org.scalatest.RecoverMethods._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.ExecutionContext.Implicits.global

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new IllegalStateException }
     | }
res0: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res0.value
res1: Option[scala.util.Try[org.scalatest.Assertion]] = Some(Success(Succeeded))

Otherwise it fails with an error message similar to those given by assertThrows:

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { throw new RuntimeException }
     | }
res2: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res2.value
res3: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but java.lang.RuntimeException
      was thrown))

scala> recoverToSucceededIf[IllegalStateException] {
     |   Future { 42 }
     | }
res4: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res4.value
res5: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: Expected exception
      java.lang.IllegalStateException to be thrown, but no exception was thrown))

The recoverToExceptionIf method differs from the recoverToSucceededIf in its behavior when the assertion succeeds: recoverToSucceededIf yields a Future[Assertion], whereas recoverToExceptionIf yields a Future[T], where T is the expected exception type.

recoverToExceptionIf[IllegalStateException] { // Result type: Future[IllegalStateException]
  emptyStackActor ? Peek
}

In other words, recoverToExpectionIf is to intercept as recovertToSucceededIf is to assertThrows. The first one allows you to perform further assertions on the expected exception. The second one gives you a result type that will satisfy the type checker at the end of the test body. Here's an example showing recoverToExceptionIf in the REPL:

scala> val futureEx =
     |   recoverToExceptionIf[IllegalStateException] {
     |     Future { throw new IllegalStateException("hello") }
     |   }
futureEx: scala.concurrent.Future[IllegalStateException] = ...

scala> futureEx.value
res6: Option[scala.util.Try[IllegalStateException]] =
    Some(Success(java.lang.IllegalStateException: hello))

scala> futureEx map { ex => assert(ex.getMessage == "world") }
res7: scala.concurrent.Future[org.scalatest.Assertion] = ...

scala> res7.value
res8: Option[scala.util.Try[org.scalatest.Assertion]] =
    Some(Failure(org.scalatest.exceptions.TestFailedException: "[hello]" did not equal "[world]"))

trait Reporter extends AnyRef

Trait whose instances collect the results of a running suite of tests and presents those results in some way to the user.

Trait whose instances collect the results of a running suite of tests and presents those results in some way to the user. Instances of this trait can be called "report functions" or "reporters."

Reporters receive test results via fifteen events. Each event is fired to pass a particular kind of information to the reporter. The events are:

Reporters may be implemented such that they only present some of the reported events to the user. For example, you could define a reporter class that does nothing in response to SuiteStarting events. Such a class would always ignore SuiteStarting events.

The term test as used in the TestStarting, TestSucceeded, and TestFailed event names is defined abstractly to enable a wide range of test implementations. ScalaTest's style traits (subclasse of trait Suite) fire TestStarting to indicate they are about to invoke one of their tests, TestSucceeded to indicate a test returned normally, and TestFailed to indicate a test completed abruptly with an exception. Although the execution of a Suite subclass's tests will likely be a common event reported via the TestStarting, TestSucceeded, and TestFailed events, because of the abstract definition of “test” used by the the event classes, these events are not limited to this use. Information about any conceptual test may be reported via the TestStarting, TestSucceeded, and TestFailed events.

Likewise, the term suite as used in the SuiteStarting, SuiteAborted, and SuiteCompleted event names is defined abstractly to enable a wide range of suite implementations. Object Runner fires SuiteStarting to indicate it is about to invoke run on a Suite, SuiteCompleted to indicate a Suite's run method returned normally, and SuiteAborted to indicate a Suite's run method completed abruptly with an exception. Similarly, class Suite fires SuiteStarting to indicate it is about to invoke run on a nested Suite, SuiteCompleted to indicate a nested Suite's run method returned normally, and SuiteAborted to indicate a nested Suite's run method completed abruptly with an exception. Although the execution of a Suite's run method will likely be a common event reported via the SuiteStarting, SuiteAborted, and SuiteCompleted events, because of the abstract definition of "suite" used by the event classes, these events are not limited to this use. Information about any conceptual suite may be reported via the SuiteStarting, SuiteAborted, and SuiteCompleted events.

Extensibility

You can create classes that extend Reporter to report test results in custom ways, and to report custom information passed as an event "payload." Reporter classes can handle events in any manner, including doing nothing.

trait ResourcefulReporter extends Reporter

Subtrait of Reporter that contains a dispose method for releasing any finite, non-memory resources, such as file handles, held by the Reporter.

Subtrait of Reporter that contains a dispose method for releasing any finite, non-memory resources, such as file handles, held by the Reporter. Runner will invoke dispose on any ResourcefulReporter when it no longer needs the Reporter.

trait Retries extends AnyRef

Provides methods that can be used in withFixture implementations to retry tests in various scenarios.

Trait Retries is intended to help you deal with “flickers”—tests that usually pass, but occasionally fail. The best way to deal with such tests is to fix them so they always pass. Sometimes, however, this is not practical. In such cases, flickers can waste your time by forcing you to investigate test failures that turn out to be flickers. Or worse, like the boy who cried wolf, the flickers may train you an your colleagues to not pay attention to failures such that you don't notice real problems, at least not in a timely manner.

Trait Retries offers methods that will retry a failed and/or canceled test once, on the same thread, with or without a delay. These methods take a block that results in Outcome, and are intended to be used in withFixture methods. You should be very selective about which tests you retry, retrying those for which you have good evidence to conclude they are flickers. Thus it is recommended you only retry tests that are tagged with Retryable, and only tag tests as such once they have flickered consistently for a while, and only after you invested a reasonable effort into fixing them properly.

Here's an example showing how you might use Retries:

package org.scalatest.examples.tagobjects.retryable

import org.scalatest._
import tagobjects.Retryable

class SetSpec extends FlatSpec with Retries {

  override def withFixture(test: NoArgTest) = {
    if (isRetryable(test))
      withRetry { super.withFixture(test) }
    else
      super.withFixture(test)
  }

  "An empty Set" should "have size 0" taggedAs(Retryable) in {
    assert(Set.empty.size === 0)
  }
}

class Sequential extends Suite with SequentialNestedSuiteExecution

A Suite class mixing in SequentialNestedSuiteExecution that takes zero to many Suites, which will be returned from its nestedSuites method.

For example, you can define a suite that always executes a list of nested suites like this:

class StepsSuite extends Sequential(
  new Step1Suite,
  new Step2Suite,
  new Step3Suite,
  new Step4Suite,
  new Step5Suite
)

When StepsSuite is executed, it will execute its nested suites in the passed order: Step1Suite, Step2Suite, Step3Suite, Step4Suite, and Step5Suite. Because Sequential extends SequentialNestedSuiteExecution, the distributor passed to runNestedSuites will always be None. So not only will the suites passed to the constructor be executed sequentially, any tests and nested suites of the passed suites will also be executed sequentually.

The difference between Sequential and Stepwise is that although Stepwise executes its own nested suites sequentially, it passes whatever distributor was passed to it to those nested suites. Thus the nested suites could run their own nested suites and tests in parallel if that distributor is defined. By contrast, Sequential always passes None for the distributor to the nested suites, so any and every test and nested suite contained within the nested suites passed to the Sequential construtor will be executed sequentially.

Exceptions thrown: NullArgumentException if suitesToNest, or any suite it contains, is null.

trait SequentialNestedSuiteExecution extends SuiteMixin

Trait that causes the nested suites of any suite it is mixed into to be run sequentially even if a Distributor is passed to runNestedSuites.

Trait that causes the nested suites of any suite it is mixed into to be run sequentially even if a Distributor is passed to runNestedSuites. This trait overrides the runNestedSuites method and fowards every parameter passed to it to a superclass invocation of runNestedSuites, except it always passes None for the Distributor. Mix in this trait into any suite whose nested suites need to be run sequentially even with the rest of the run is being executed concurrently.

trait SeveredStackTraces extends TestSuiteMixin

Trait that causes StackDepth exceptions thrown by a running test (such as TestFailedExceptions) to have the exception's stack trace severed at the stack depth.

Trait that causes StackDepth exceptions thrown by a running test (such as TestFailedExceptions) to have the exception's stack trace severed at the stack depth. Because the stack depth indicates the exact line of code that caused the exception to be thrown, the severed stack trace will show that offending line of code on top. This can make the line of test code that discovered a problem to be more easily found in IDEs and tools that don't make use of ScalaTest's StackDepth exceptions directly.

sealed trait Shell extends AnyRef

Trait whose instances provide a run method and configuration fields that implement the ScalaTest shell: its DSL for the Scala interpreter.

The main command of the ScalaTest shell is run, which you can use to run a suite of tests. The shell also provides several commands for configuring a call to run:

color (the default) - display results in color (green for success; red for failure; yellow for warning; blue for statistics)
nocolor - display results without color
durations - display durations of (i.e., how long it took to run) tests and suites
nodurations (the default) - do not display durations of tests and suites
shortstacks - display short (i.e., truncated to show just the most useful portion) stack traces for all exceptions
fullstacks - display full stack trackes for all exceptions
nostacks (the default) - display no stack trace for StackDepth exceptions and a short stack trace for non-StackDepth exceptions
stats - display statistics before and after the run, such as expected test count before the run and tests succeeded, failed, pending, etc., counts after the run
nostats (the default) not display statistics before or after the run

The default configuration is color, nodurations, nostacks, and nostats.

All of these commands are fields of trait org.scalatest.Shell. Each configuration command is a field that refers to another Shell instance with every configuration parameter the same except for the one you've asked to change. For example, durations provides a Shell instance that has every parameter configured the same way, except with durations enabled. When you invoke run on that, you will get a run with durations enabled and every other configuration parameter at its default value.

The other useful "command" to know about, though not technically part of the shell, is the apply factory method in the Suites singleton object. This allows you to easily create composite suites out of nested suites, which you can then pass to run. This will be demonstrated later in this documentation.

Using the ScalaTest shell

The package object of the org.scalatest package, although it does not extend Shell, declares all the same members as Shell. Its run method runs with all the Shell configuration parameters set to their default values. A good way to use the ScalaTest shell, therefore, is to import the members of package org.scalatest:

scala> import org.scalatest._
import org.scalatest._

One thing importing org.scalatest._ allows you to do is access any of ScalaTest's classes and traits by shorter names, for example:

scala> class ArithmeticSuite extends FunSuite with matchers.Matchers {
     |   test("addition works") {
     |     1 + 1 should equal (2)
     |   }
     |   ignore("subtraction works") {
     |     1 - 1 should equal (0)
     |   }
     |   test("multiplication works") {
     |     1 * 1 should equal (2)
     |   }
     |   test("division works") (pending)
     | }
defined class ArithmeticSuite

But importing org.scalatest._ also brings into scope the commands of the Shell, so you can, for example, invoke run without qualification:

scala> run(new ArithmeticSuite)
ArithmeticSuite:
- addition works
- subtraction works !!! IGNORED !!!
- multiplication works *** FAILED ***
  1 did not equal 2 (:16)
- division works (pending)

Configuring a single run

To configure a single run, you can prefix run by one or more configuration commands, separated by dots. For example, to enable durations during a single run, you would write:

scala> durations.run(new ArithmeticSuite)
ArithmeticSuite:
- addition works (102 milliseconds)
- subtraction works !!! IGNORED !!!
- multiplication works *** FAILED *** (36 milliseconds)
  1 did not equal 2 (:16)
- division works (pending)

To enable statistics during a single run, you would write:

scala> stats.run(new ArithmeticSuite)
Run starting. Expected test count is: 3
ArithmeticSuite:
- addition works
- subtraction works !!! IGNORED !!!
- multiplication works *** FAILED ***
  1 did not equal 2 (:16)
- division works (pending)
Run completed in 386 milliseconds.
Total number of tests run: 2
Suites: completed 1, aborted 0
Tests: succeeded 1, failed 1, ignored 1, pending 1
*** 1 TEST FAILED ***

And to enable both durations and statistics during a single run, you could write:

scala> durations.stats.run(new ArithmeticSuite)
Run starting. Expected test count is: 3
ArithmeticSuite:
- addition works (102 milliseconds)
- subtraction works !!! IGNORED !!!
- multiplication works *** FAILED (36 milliseconds)***
  1 did not equal 2 (:16)
- division works (pending)
Run completed in 386 milliseconds.
Total number of tests run: 2
Suites: completed 1, aborted 0
Tests: succeeded 1, failed 1, ignored 1, pending 1
*** 1 TEST FAILED ***

The order doesn't matter when you are chaining multiple configuration commands. You'll get the same result whether you write durations.stats.run or stats.durations.run.

To disable color, use nocolor:

scala> nocolor.run(new ArithmeticSuite)
ArithmeticSuite:
- addition works
- subtraction works !!! IGNORED !!!
- multiplication works *** FAILED ***
  1 did not equal 2 (:16)
- division works (pending)

To enable short stack traces during a single run, use shortstacks:

scala> shortstacks.run(new ArithmeticSuite)
ArithmeticSuite:
- addition works (101 milliseconds)
- subtraction works !!! IGNORED !!!
- multiplication works *** FAILED *** (33 milliseconds)
  1 did not equal 2 (:16)
  org.scalatest.exceptions.TestFailedException:
  ...
  at line2$object$$iw$$iw$$iw$$iw$ArithmeticSuite$$anonfun$3.apply$mcV$sp(:16)
  at line2$object$$iw$$iw$$iw$$iw$ArithmeticSuite$$anonfun$3.apply(:16)
  at line2$object$$iw$$iw$$iw$$iw$ArithmeticSuite$$anonfun$3.apply(:16)
  at org.scalatest.FunSuite$$anon$1.apply(FunSuite.scala:992)
  at org.scalatest.Suite$class.withFixture(Suite.scala:1661)
  at line2$object$$iw$$iw$$iw$$iw$ArithmeticSuite.withFixture(:8)
  at org.scalatest.FunSuite$class.invokeWithFixture$1(FunSuite.scala:989)
  ...
- division works (pending)

Changing the default configuration

If you want to change the default for multiple runs, you can import the members of your favorite Shell configuration. For example, if you always like to run with durations and statistics enabled, you could write:

scala> import stats.durations._
import stats.durations._

Now anytime you run statistics and durations will, by default, be enabled:

scala> run(new ArithmeticSuite)
Run starting. Expected test count is: 3
ArithmeticSuite:
- addition works (9 milliseconds)
- subtraction works !!! IGNORED !!!
- multiplication works *** FAILED *** (10 milliseconds)
  1 did not equal 2 (:18)
- division works (pending)
Run completed in 56 milliseconds.
Total number of tests run: 2
Suites: completed 1, aborted 0
Tests: succeeded 1, failed 1, ignored 1, pending 1
*** 1 TEST FAILED ***

Running multiple suites

If you want to run multiple suites, you can use the factory method in the Suites singleton object. If you wrap a comma-separated list of suite instances inside Suites(...), for example, you'll get a suite instance that contains no tests, but whose nested suites includes the suite instances you placed between the parentheses. You can place Suites inside Suites to any level of depth, creating a tree of suites to pass to run. Here's a (contrived) example in which ArithmeticSuite is executed four times:

scala> run(Suites(new ArithmeticSuite, new ArithmeticSuite, Suites(new ArithmeticSuite, new ArithmeticSuite)))
Run starting. Expected test count is: 12
Suites:
ArithmeticSuite:
- addition works (0 milliseconds)
- subtraction works !!! IGNORED !!!
- multiplication works *** FAILED *** (1 millisecond)
  1 did not equal 2 (:16)
- division works (pending)
ArithmeticSuite:
- addition works (1 millisecond)
- subtraction works !!! IGNORED !!!
- multiplication works *** FAILED *** (0 milliseconds)
  1 did not equal 2 (:16)
- division works (pending)
Suites:
ArithmeticSuite:
- addition works (0 milliseconds)
- subtraction works !!! IGNORED !!!
- multiplication works *** FAILED *** (0 milliseconds)
  1 did not equal 2 (:16)
- division works (pending)
ArithmeticSuite:
- addition works (0 milliseconds)
- subtraction works !!! IGNORED !!!
- multiplication works *** FAILED *** (0 milliseconds)
  1 did not equal 2 (:16)
- division works (pending)
Run completed in 144 milliseconds.
Total number of tests run: 8
Suites: completed 6, aborted 0
Tests: succeeded 4, failed 4, ignored 4, pending 4
*** 4 TESTS FAILED ***

Running a single test

The run command also allows you to specify the name of a test to run and/or a config map. You can run a particular test in a suite, for example, by specifying the test name after the suite instance in your call to run, like this:

scala> run(new ArithmeticSuite, "addition works")
ArithmeticSuite:
- addition works

final class StatefulStatus extends Status with Serializable

Status implementation that can change its state over time.

A StatefulStatus begins its life in a successful state, and will remain successful unless setFailed is called. Once setFailed is called, the status will remain at failed. The setFailed method can be called multiple times (even though invoking it once is sufficient to permanently set the status to failed), but only up until setCompleted has been called. After setCompleted has been called, any invocation of setFailed will be greeted with an IllegalStateException.

Instances of this class are thread safe.

sealed trait Status extends AnyRef

The result status of running a test or a suite, which is used to support parallel and asynchronous execution of tests.

This trait is the result type of the "run" lifecycle methods of trait Suite: run, runNestedSuites, runTests, and runTest. It can be used to determine whether a test or suite has completed, and if so, whether it succeeded, and if not, whether an exception was thrown that was not yet reported via a ScalaTest event. A Status is like a domain-specific Future[Boolean], where:

an activity in which no test failed and no suite aborted is represented by Success(true)
an activity during which at least one test failed or one suite aborted, but all exceptions that occured were reported by a ScalaTest events (such as TestFailedException) is represented by Success(false)
an activity during which at least one test failed or one suite aborted and at least one exception occurred that was not reported via a ScalaTest event is represented by Failure(unreportedException)

Note that pending and canceled tests will not cause a Status to fail. Only failed tests and aborted suites will cause a Status to fail.

One use case of Status is to ensure that "after" code (such as an afterEach or afterAll method) does not execute until after the relevant entity (one test, one suite, or all of a suite's tests or nested suites) has completed. Another use case is to implement the default behavior of asynchronous styles, in which subsequent each test does not begin execution until after the previous test has completed.

class Stepwise extends Suite with StepwiseNestedSuiteExecution

A Suite class that takes zero to many Suites, which will be returned from its nestedSuites method and executed in “stepwise” fashion by its runNestedSuites method.

For example, you can define a suite that always executes a list of nested suites like this:

class StepsSuite extends Stepwise(
  new Step1Suite,
  new Step2Suite,
  new Step3Suite,
  new Step4Suite,
  new Step5Suite
)

When StepsSuite is executed, regardless of whether a Distributor is passed, it will execute its nested suites sequentially in the passed order: Step1Suite, Step2Suite, Step3Suite, Step4Suite, and Step5Suite.

The difference between Stepwise and Sequential is that although Stepwise executes its own nested suites sequentially, it passes whatever distributor was passed to it to those nested suites. Thus the nested suites could run their own nested suites and tests in parallel if that distributor is defined. By contrast, Sequential always passes None for the distributor to the nested suites, so any and every test and nested suite contained within the nested suites passed to the Sequential construtor will be executed sequentially.

Exceptions thrown: NullArgumentException if suitesToNest, or any suite it contains, is null.

trait StepwiseNestedSuiteExecution extends SuiteMixin

Trait that causes the nested suites of any suite it is mixed into to be run sequentially even if a Distributor is passed to runNestedSuites.

Trait that causes the nested suites of any suite it is mixed into to be run sequentially even if a Distributor is passed to runNestedSuites. This trait overrides the runNestedSuites method and fowards every parameter passed to it to a superclass invocation of runNestedSuites, except it always passes None for the Distributor. Mix in this trait into any suite whose nested suites need to be run sequentially even with the rest of the run is being executed concurrently.

trait Stopper extends AnyRef

Trait whose instances can accept a stop request and indicate whether a stop has already been requested.

This is passed in to the run method of Suite, so that running suites of tests can be requested to stop early.

trait StreamlinedXml extends AnyRef

Trait providing a streamlined method that returns a Uniformity[T] instance for any subtype of scala.xml.NodeSeq that will normalize the XML by removing empty text nodes and trimming non-empty text nodes.

Here's an example of some unnormalized XML:

<summer>
  <day></day>
  <night>
    with lots of stars
  </night>
</summer>

The Uniformity returned by this trait's streamlined method would transform the above XML to:

<summer><day></day><night>with lots of stars</night></summer>

The streamlined method can be used with the Explicitly DSL, like this:

xmlElem should equal (
  <summer>
    <day></day>
    <night>
      with lots of stars
    </night>
  </summer>
) (after being streamlined[Elem])

The goal of this trait is to provide a normalization for XML that makes it easier to test XML objects for equality. White space is significant in XML, and is taken into account by the default equality for XML, accessed by invoking the == method on an XML NodeSeq. Here's an example:

scala> val xmlElem = <summer><day></day><night>with lots of stars</night></summer>
xmlElem: scala.xml.Elem = <summer><day></day><night>with lots of stars</night></summer>

scala> xmlElem == <summer>
     |   <day></day>
     |   <night>
     |     with lots of stars
     |   </night>
     | </summer>
res1: Boolean = false

The above equality comparison produces false because of whitespace differences in the XML. When such whitespace differences are unimportant to the actual application, it can make it easier to write readable test code if you can compare XML for equality without taking into account empty text nodes, or leading and trailing whitespace in nonempty text nodes. The streamlined method of this trait provides a Uniformity instance that does just that:

scala> import org.scalactic._
import org.scalactic._

scala> import Explicitly._
import Explicitly._

scala> import TripleEquals._
import TripleEquals._

scala> import org.scalatest.StreamlinedXml._
import StreamlinedXml._

scala> import scala.xml.Elem
import scala.xml.Elem *

scala> (xmlElem === <summer>
     |   <day></day>
     |   <night>
     |     with lots of stars
     |   </night>
     | </summer>) (after being streamlined[Elem])
res9: Boolean = true

trait StreamlinedXmlEquality extends AnyRef

Trait providing an implicit Equality[T] for subtypes of scala.xml.NodeSeq that before testing for equality, will normalize left and right sides by removing empty XML text nodes and trimming non-empty text nodes.

Here's an example of some unnormalized XML:

<summer>
  <day></day>
  <night>
    with lots of stars
  </night>
</summer>

Prior to testing it for equality, the implicit Equality[T] provided by this trait would transform the above XML to:

<summer><day></day><night>with lots of stars</night></summer>

The goal of this trait is to provide an implicit Equality for XML that makes it easier to write tests involving XML. White space is significant in XML, and is taken into account by the default equality for XML, accessed by invoking the == method on an XML NodeSeq. Here's an example:

scala> val xmlElem = <summer><day></day><night>with lots of stars</night></summer>
xmlElem: scala.xml.Elem = <summer><day></day><night>with lots of stars</night></summer>

scala> import org.scalatest.Assertions._
import org.scalatest.Assertions._

scala> assert(xmlElem === <summer>
     |   <day></day>
     |     <night>
     |       with lots of stars
     |     </night>
     |   </summer>)
org.scalatest.exceptions.TestFailedException: <summer><day></day><night>with lots of stars</night></summer> did not equal <summer>
  <day></day>
    <night>
      with lots of stars
    </night>
  </summer>
  at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:500)
  at org.scalatest.Assertions$.newAssertionFailedException(Assertions.scala:1538)
  at org.scalatest.Assertions$AssertionsHelper.macroAssert(Assertions.scala:466)
  ... 53 elided

The above assertion fails because of whitespace differences in the XML. When such whitespace differences are unimportant to the actual application, it can make it easier to write readable test code if you can compare XML for equality without taking into account empty text nodes, or leading and trailing whitespace in nonempty text nodes. This trait provides an Equality[T] instance that does just that:

scala> import org.scalatest.StreamlinedXmlEquality._
import org.scalatest.StreamlinedXmlEquality._

scala> assert(xmlElem === <summer>
     |   <day></day>
     |   <night>
     |     with lots of stars
     |   </night>
     | </summer>)

trait StreamlinedXmlNormMethods extends StreamlinedXml with NormMethods

Subtrait of NormMethods that provides an implicit Uniformity[T] for subtypes of scala.xml.NodeSeq that enables you to streamline XML by invoking .norm on it.

Here's an example:

scala> <good><day>sunshine</day></good> == <good>
     |   <day>
     |     sunshine
     |   </day>
     | </good>
res1: Boolean = false

scala> import org.scalactic._
import org.scalactic._

scala> import TripleEquals._
import TripleEquals._

scala> import org.scalatest.StreamlinedXmlNormMethods._
import org.scalatest.StreamlinedXmlNormMethods._

scala> <good><day>sunshine</day></good> === <good>
     |   <day>
     |     sunshine
     |   </day>
     | </good>.norm
res2: Boolean = true

trait Suite extends Assertions with Serializable

A suite of tests.

A suite of tests. A Suite instance encapsulates a conceptual suite (i.e., a collection) of tests.

This trait provides an interface composed of "lifecycle methods" that allow suites of tests to be run. Its implementation enables a default way of writing and executing tests. Subtraits and subclasses can override Suite's lifecycle methods to enable other ways of writing and executing tests.

Nested suites

A Suite can refer to a collection of other Suites, which are called nested Suites. Those nested Suites can in turn have their own nested Suites, and so on. Large test suites can be organized, therefore, as a tree of nested Suites. This trait's run method, in addition to invoking its test methods, invokes run on each of its nested Suites.

A List of a Suite's nested Suites can be obtained by invoking its nestedSuites method. If you wish to create a Suite that serves as a container for nested Suites, whether or not it has test methods of its own, simply override nestedSuites to return a List of the nested Suites. Because this is a common use case, ScalaTest provides a convenience Suites class, which takes a variable number of nested Suites as constructor parameters. Here's an example:

package org.scalatest.examples.suite.nested

import org.scalatest._

class ASuite extends FunSuite {
  test("A should have ASCII value 41 hex") {
    assert('A' === 0x41)
  }
  test("a should have ASCII value 61 hex") {
    assert('a' === 0x61)
  }
}
class BSuite extends FunSuite {
  test("B should have ASCII value 42 hex") {
    assert('B' === 0x42)
  }
  test("b should have ASCII value 62 hex") {
    assert('b' === 0x62)
  }
}
class CSuite extends FunSuite {
  test("C should have ASCII value 43 hex") {
    assert('C' === 0x43)
  }
  test("c should have ASCII value 63 hex") {
    assert('c' === 0x63)
  }
}

class ASCIISuite extends Suites(
  new ASuite,
  new BSuite,
  new CSuite
)

If you now run ASCIISuite:

scala> org.scalatest.run(new ASCIISuite)

You will see reports printed to the standard output that indicate the nested suites—ASuite, BSuite, and CSuite—were run:

ASCIISuite:
ASuite:
- A should have ASCII value 41 hex
- a should have ASCII value 61 hex
BSuite:
- B should have ASCII value 42 hex
- b should have ASCII value 62 hex
CSuite:
- C should have ASCII value 43 hex
- c should have ASCII value 63 hex

Note that Runner can discover Suites automatically, so you need not necessarily define nested Suites explicitly. See the documentation for Runner for more information.

The config map

In some cases you may need to pass information to a suite of tests. For example, perhaps a suite of tests needs to grab information from a file, and you want to be able to specify a different filename during different runs. You can accomplish this in ScalaTest by passing the filename in a config map of key-value pairs, which is passed to run as a ConfigMap. The values in the config map are called "config objects," because they can be used to configure suites, reporters, and tests.

You can specify a string config object is via the ScalaTest Runner, either via the command line or ScalaTest's ant task. (See the documentation for Runner for information on how to specify config objects on the command line.) The config map is passed to run, runNestedSuites, runTests, and runTest, so one way to access it in your suite is to override one of those methods. If you need to use the config map inside your tests, you can access it from the NoArgTest passed to withFixture, or the OneArgTest passed to withFixture in the traits in the org.scalatest.fixture package. (See the documentation for fixture.Suite for instructions on how to access the config map in tests.)

Executing suites in parallel

The run method takes as one of its parameters an optional Distributor. If a Distributor is passed in, this trait's implementation of run puts its nested Suites into the distributor rather than executing them directly. The caller of run is responsible for ensuring that some entity runs the Suites placed into the distributor. The -P command line parameter to Runner, for example, will cause Suites put into the Distributor to be run in parallel via a pool of threads. If you wish to execute the tests themselves in parallel, mix in ParallelTestExecution.

"Run-aborting" exceptions

The Javadoc documentation for java.lang.Error states:

An Error is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch. Most such errors are abnormal conditions.

Because Errors are used to denote serious errors, trait Suite and its subtypes in the ScalaTest API do not always treat a test that completes abruptly with an Error as a test failure, but sometimes as an indication that serious problems have arisen that should cause the run to abort. For example, if a test completes abruptly with an OutOfMemoryError, it will not be reported as a test failure, but will instead cause the run to abort. Because not everyone uses Errors only to represent serious problems, however, ScalaTest only behaves this way for the following run-aborting exception types (and their subclasses):

java.lang.annotation.AnnotationFormatError
java.awt.AWTError
java.nio.charset.CoderMalfunctionError
javax.xml.parsers.FactoryConfigurationError
java.lang.LinkageError
java.lang.ThreadDeath
javax.xml.transform.TransformerFactoryConfigurationError
java.lang.VirtualMachineError

The previous list includes all Errors that exist as part of Java 1.5 API, excluding java.lang.AssertionError. ScalaTest does treat a thrown AssertionError as an indication of a test failure. In addition, any other Error that is not an instance of a type mentioned in the previous list will be caught by the Suite traits in the ScalaTest API and reported as the cause of a test failure.

Although trait Suite and all its subtypes in the ScalaTest API consistently behave this way with regard to Errors, this behavior is not required by the contract of Suite. Subclasses and subtraits that you define, for example, may treat all Errors as test failures, or indicate errors in some other way that has nothing to do with exceptions.

Extensibility

Trait Suite provides default implementations of its methods that should be sufficient for most applications, but many methods can be overridden when desired. Here's a summary of the methods that are intended to be overridden:

run - override this method to define custom ways to run suites of tests.
runNestedSuites - override this method to define custom ways to run nested suites.
runTests - override this method to define custom ways to run a suite's tests.
runTest - override this method to define custom ways to run a single named test.
testNames - override this method to specify the Suite's test names in a custom way.
tags - override this method to specify the Suite's test tags in a custom way.
nestedSuites - override this method to specify the Suite's nested Suites in a custom way.
suiteName - override this method to specify the Suite's name in a custom way.
expectedTestCount - override this method to count this Suite's expected tests in a custom way.

For example, this trait's implementation of testNames performs reflection to discover methods starting with test, and places these in a Set whose iterator returns the names in alphabetical order. If you wish to run tests in a different order in a particular Suite, perhaps because a test named testAlpha can only succeed after a test named testBeta has run, you can override testNames so that it returns a Set whose iterator returns testBeta before testAlpha. (This trait's implementation of run will invoke tests in the order they come out of the testNames Set iterator.)

Alternatively, you may not like starting your test methods with test, and prefer using @Test annotations in the style of Java's JUnit 4 or TestNG. If so, you can override testNames to discover tests using either of these two APIs @Test annotations, or one of your own invention. (This is in fact how org.scalatest.junit.JUnitSuite and org.scalatest.testng.TestNGSuite work.)

Moreover, test in ScalaTest does not necessarily mean test method. A test can be anything that can be given a name, that starts and either succeeds or fails, and can be ignored. In org.scalatest.FunSuite, for example, tests are represented as function values. This approach might look foreign to JUnit users, but may feel more natural to programmers with a functional programming background. To facilitate this style of writing tests, FunSuite overrides testNames, runTest, and run such that you can define tests as function values.

You can also model existing JUnit 3, JUnit 4, or TestNG tests as suites of tests, thereby incorporating tests written in Java into a ScalaTest suite. The "wrapper" classes in packages org.scalatest.junit and org.scalatest.testng exist to make this easy. No matter what legacy tests you may have, it is likely you can create or use an existing Suite subclass that allows you to model those tests as ScalaTest suites and tests and incorporate them into a ScalaTest suite. You can then write new tests in Scala and continue supporting older tests in Java.

trait SuiteMixin extends AnyRef

Trait defining abstract "lifecycle" methods that are implemented in Suite and can be overridden in stackable modification traits.

The main purpose of SuiteMixin is to differentiate core Suite style traits, such as Spec, FunSuite, and FunSpec from stackable modification traits for Suites such as BeforeAndAfterEach, OneInstancePerTest, and SequentialNestedSuiteExecution. Because these stackable traits extend SuiteMixin instead of Suite, you can't define a suite by simply extending one of the stackable traits:

class MySuite extends BeforeAndAfterEach // Won't compile

Instead, you need to extend a core Suite trait and mix the stackable BeforeAndAfterEach trait into that, like this:

class MySuite extends FunSuite with BeforeAndAfterEach // Compiles fine

class Suites extends Suite

A Suite class that takes zero to many Suites in its constructor, which will be returned from its nestedSuites method.

For example, you can define a suite that always executes a list of nested suites like this:

class StepsSuite extends Suites(
  new Step1Suite,
  new Step2Suite,
  new Step3Suite,
  new Step4Suite,
  new Step5Suite
)

If StepsSuite is executed sequentially, it will execute its nested suites in the passed order: Step1Suite, Step2Suite, Step3Suite, Step4Suite, and Step5Suite. If StepsSuite is executed in parallel, the nested suites will be executed concurrently.

Exceptions thrown: NullPointerException if suitesToNest, or any suite it contains, is null.

class Tag extends AnyRef

Class whose subclasses can be used to tag tests in style traits in which tests are defined as functions.

ScalaTest has two ways to tag tests: annotations and instances of this Tag class. To tag a test method or an entire test class, you use a tag annotation, whereas to tag a test function, you use a Tag object. Though not required, it is usually a good idea to define both an annotation and a corresponding Tag object for each conceptual tag you want, so you can tag anything: test functions, test classes, and test methods. The name of the conceptual tag is the fully qualified name of the annotation interface, so you must pass this name to the Tag constructor.

For example, imagine you want to tag integration tests that use the actual database, and are, therefore, generally slower. You could create a tag annotation and object called DbTest. To give them both the same simple name, you can declare them in different packages. The tag annotation must be written in Java, not Scala, because annotations written in Scala are not accessible at runtime. Here's an example:

package com.mycompany.myproject.testing.tags;

import java.lang.annotation.*;
import org.scalatest.TagAnnotation

@TagAnnotation
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.TYPE})
public @interface DbTest {}

Given this annotation's fully qualified name is com.mycompany.myproject.testing.tags.DbTest the corresponding Tag object decaration must have that name passed to its constructor, like this:

package com.mycompany.myproject.testing.tagobjects

object DbTest extends Tag("com.mycompany.myproject.testing.tags.DbTest")

Given these definitions, you could tag a test function as a DbTest in, for example, a FlatSpec like this:

import org.scalatest.FlatSpec
import com.mycompany.myproject.testing.tagobjects.DbTest

class ExampleSpec extends FlatSpec {

  "Integration tests" can "sometimes be slow" taggedAs(DbTest) in {
    Thread.sleep(1000)
  }
}

You could tag a test method as a DbTest in, for example, a Suite like this:

import org.scalatest.Suite
import com.mycompany.myproject.testing.tags.DbTest

class ExampleSuite extends Suite {

  @DbTest
  def `integration tests can sometimes be slow` {
    Thread.sleep(1000)
  }
}

And you could tag all the tests in an entire test class by annotating the class, like this:

import org.scalatest.FlatSpec
import com.mycompany.myproject.testing.tags.DbTest

@DBTest
class ExampleSpec extends FlatSpec {

  "Integration tests" can "sometimes be slow" in {
    Thread.sleep(1000)
  }

  they should "likely sometimes be excluded " in {
    Thread.sleep(1000)
  }
}

In the previous example, both tests will be tagged as DBTests even though the tests are not tagged as such individually.

When you run ScalaTest and want to either include or exclude DbTests, you'd give the fully qualified name of the tag annotation (which is also the name passed to the corresponding Tag constructor) to Runner. For example, here's how you'd exclude DbTests on the Runner command line:

-l com.mycompany.myproject.testing.tags.DbTest

For examples of tagging in other style traits, see the "Tagging tests" section in the documentation for the trait:

trait TagAnnotation extends Annotation

Annotation used to annotate annotation interfaces that define tags for ScalaTest tests.

Note: This is actually an annotation defined in Java, not a Scala trait. It must be defined in Java instead of Scala so it will be accessible at runtime. It has been inserted into Scaladoc by pretending it is a trait.

ScalaTest will only consider annotations that are themselves annotated with TagAnnotation as tag annotations, to avoid accidentally interpreting arbitrary annotations as tags. You use TagAnnotation, therefore, when you define a tag annotation (which you must do in Java). Here's an example:

package com.mycompany.myproject.testing.tags;

import java.lang.annotation.*;
import org.scalatest.TagAnnotation *

@TagAnnotation
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.TYPE})
public @interface DbTest {}

For more information, see the documentation for class Tag.

trait TestData extends AnyRef

A bundle of information about the current test.

A TestData object is passed to the withFixture methods of traits Suite and fixture.Suite (both NoArgTest and OneArgTest extend TestData) and to the beforeEach and afterEach methods of trait BeforeAndAfterEach. This enables fixtures and tests to make use of the test name and configuration objects in the config map.

In ScalaTest's event model, a test may be surrounded by “scopes.” Each test and scope is associated with string of text. A test's name is a concatenation of the text of any surrounding scopes followed by the text provided with the test itself, after each text element has been trimmed and one space inserted between each component. Here's an example:

package org.scalatest.examples.freespec

import org.scalatest.FreeSpec

class SetSpec extends FreeSpec {

  "A Set" - {
    "when empty" - {
      "should have size 0" in {
        assert(Set.empty.size === 0)
      }

      "should produce NoSuchElementException when head is invoked" in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

The above FreeSpec contains two tests, both nested inside the same two scopes. The outermost scope names the subject, A Set. The nested scope qualifies the subject with when empty. Inside that scope are the two tests. The text of the tests are:

should have size 0
should produce NoSuchElementException when head is invoked

Therefore, the names of these two tests are:

A Stack when empty should have size 0
A Stack when empty should produce NoSuchElementException when head is invoked

The TestData instance for the first test would contain:

name: "A Stack when empty should have size 0"
scopes: collection.immutable.IndexedSeq("A Stack", "when empty")
text: "should have size 0"

trait TestRegistration extends AnyRef

Trait declaring methods that can be used to register by-name test functions that have any result type.

trait TestSuite extends Suite

The base trait of ScalaTest's synchronous testing styles, which defines a withFixture lifecycle method that accepts as its parameter a test function that returns an Outcome.

The withFixture method add by this trait has the following signature and implementation:

def withFixture(test: NoArgTest): Outcome = {
  test()
}

The apply method of test function interface, NoArgTest, also returns Outcome:

// In trait NoArgTest:
def apply(): Outcome

Because the result of a test is an Outcome, when the test function returns, the test body must have determined an outcome already. It will already be one of Succeeded, Failed, Canceled, or Pending. This is also true when withFixture(NoArgTest) returns: because the result type of withFixture(NoArgTest) is Outcome, the test has by definition already finished execution.

The recommended way to ensure cleanup is performed after a test body finishes execution is to use a try-finally clause. Using try-finally will ensure that cleanup will occur whether the test function completes abruptly by throwing a suite-aborting exception, or returns normally yielding an Outcome. Note that the only situation in which a test function will complete abruptly with an exception is if the test body throws a suite-aborting exception. Any other exception will be caught and reported as either a Failed, Canceled, or Pending.

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. In other words, instead of writing “test()”, you should write “super.withFixture(test)”. Thus, the recommended structure of a withFixture implementation that performs cleanup looks like this:

// Your implementation
override def withFixture(test: NoArgTest) = {
  // Perform setup here
  try {
    super.withFixture(test) // Invoke the test function
  } finally {
    // Perform cleanup here
  }
}

If you have no cleanup to perform, you can write withFixture like this instead:

// Your implementation
override def withFixture(test: NoArgTest) = {
  // Perform setup here
  super.withFixture(test) // Invoke the test function
}

If you want to perform an action only for certain outcomes, you can use a pattern match. For example, if you want to perform an action if a test fails, you'd match on Failed, like this:

// Your implementation
override def withFixture(test: NoArgTest) = {

  // Perform setup here

  val outcome = super.withFixture(test) // Invoke the test function

  outcome match {
    case failed: Failed =>
      // perform action that you want to occur
      // only if a test fails here
      failed
    case other => other
  }
}

If you want to change the outcome in some way in withFixture, you can also use a pattern match. For example, if a particular exception intermittently causes a test to fail, and can transform those failures into cancelations, like this:

// Your implementation
override def withFixture(test: NoArgTest) = {

  super.withFixture(test) match {
    case Failed(ex: ParticularException) =>
      Canceled("Muting flicker", ex)
    case other => other
  }
}

trait TestSuiteMixin extends SuiteMixin

final class Tracker extends AnyRef

Class that tracks the progress of a series of Ordinals produced by invoking next and nextNewOldPair on the current Ordinal.

Instances of this class are thread safe. Multiple threads can invoke nextOrdinal and nextTracker concurrently. This facilitates multi-threaded tests that send infoProvided reports concurrently. When using a Dispatcher to execute suites in parallel, the intention is that each Tracker will only be used by one thread. For example, if the optional Dispatcher passed to Suite's implementation of runNestedSuites is defined, that method will obtain a new Tracker by invoking nextTracker for each nested suite it passes to the Dispatcher.

trait TryValues extends AnyRef

Trait that provides an implicit conversion that adds success and failure methods to scala.util.Try, enabling you to make assertions about the value of a Success or the exception of a Failure.

The success method will return the Try on which it is invoked as a Success if the Try actually is a Success, or throw TestFailedException if not. The failure method will return the Try on which it is invoked as a Failure if the Try actually is a Failure, or throw TestFailedException if not.

This construct allows you to express in one statement that an Try should be either a Success or a Failure and that its value or exception, respectively,should meet some expectation. Here's an example:

try1.success.value should be > 9
try2.failure.exception should have message "/ by zero"

Or, using assertions instead of a matchers:

assert(try1.success.value > 9)
assert(try2.failure.exception.getMessage == "/ by zero")

Were you to simply invoke get on the Try, if the Try wasn't a Success, it would throw the exception contained in the Failure:

val try2 = Try { 1 / 0 }

try2.get should be < 9 // try2.get throws ArithmeticException

The ArithmeticException would cause the test to fail, but without providing a stack depth pointing to the failing line of test code. This stack depth, provided by TestFailedException (and a few other ScalaTest exceptions), makes it quicker for users to navigate to the cause of the failure. Without TryValues, to get a stack depth exception you would need to make two statements, like this:

try2 should be a 'success // throws TestFailedException
try2.get should be < 9

The TryValues trait allows you to state that more concisely:

try2.success.value should be < 9 // throws TestFailedException

class WordSpec extends WordSpecLike

Facilitates a “behavior-driven” style of development (BDD), in which tests are combined with text that specifies the behavior the tests verify.

Recommended Usage: For teams coming from specs or specs2, WordSpec will feel familiar, and is often the most natural way to port specsN tests to ScalaTest. WordSpec is very prescriptive in how text must be written, so a good fit for teams who want a high degree of discipline enforced upon their specification text.

Class WordSpec is so named because your specification text is structured by placing words after strings. Here's an example WordSpec:

package org.scalatest.examples.wordspec

import org.scalatest.WordSpec

class SetSpec extends WordSpec {

  "A Set" when {
    "empty" should {
      "have size 0" in {
        assert(Set.empty.size === 0)
      }

      "produce NoSuchElementException when head is invoked" in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

In a WordSpec you write a one (or more) sentence specification for each bit of behavior you wish to specify and test. Each specification sentence has a "subject," which is sometimes called the system under test (or SUT). The subject is entity being specified and tested and also serves as the subject of the sentences you write for each test. A subject can be followed by one of three verbs, should, must, or can, and a block. Here are some examples:

"A Stack" should {
  // ...
}
"An Account" must {
  // ...
}
"A ShippingManifest" can {
  // ...
}

You can describe a subject in varying situations by using a when clause. A when clause follows the subject and precedes a block. In the block after the when, you place strings that describe a situation or a state the subject may be in using a string, each followed by a verb. Here's an example:

"A Stack" when {
  "empty" should {
    // ...
  }
  "non-empty" should {
    // ...
  }
  "full" should {
    // ...
  }
}

When you are ready to finish a sentence, you write a string followed by in and a block that contains the code of the test. Here's an example:

import org.scalatest.WordSpec

class StackSpec extends WordSpec {
  "A Stack" when {
    "empty" should {
      "be empty" in {
        // ...
      }
      "complain on peek" in {
        // ...
      }
      "complain on pop" in {
        // ...
      }
    }
    "full" should {
      "be full" in {
        // ...
      }
      "complain on push" in {
        // ...
      }
    }
  }
}

Running the above StackSpec in the interpreter would yield:

scala> org.scalatest.run(new StackSpec)
StackSpec:
A Stack
  when empty
  - should be empty
  - should complain on peek
  - should complain on pop
  when full
  - should be full
  - should complain on push

Note that the output does not exactly match the input in an effort to maximize readability. Although the WordSpec code is nested, which can help you eliminate any repeated phrases in the specification portion of your code, the output printed moves when and should down to the beginning of the next line.

Sometimes you may wish to eliminate repeated phrases inside the block following a verb. Here's an example in which the phrase "provide an and/or operator, which" is repeated:

import org.scalatest.WordSpec

class AndOrSpec extends WordSpec {

  "The ScalaTest Matchers DSL" should {
    "provide an and operator, which returns silently when evaluating true and true" in {}
    "provide an and operator, which throws a TestFailedException when evaluating true and false" in {}
    "provide an and operator, which throws a TestFailedException when evaluating false and true" in {}
    "provide an and operator, which throws a TestFailedException when evaluating false and false" in {}
    "provide an or operator, which returns silently when evaluating true or true" in {}
    "provide an or operator, which returns silently when evaluating true or false" in {}
    "provide an or operator, which returns silently when evaluating false or true" in {}
    "provide an or operator, which throws a TestFailedException when evaluating false or false" in {}
  }
}

In such situations you can place which clauses inside the verb clause, like this:

import org.scalatest.WordSpec

class AndOrSpec extends WordSpec {

  "The ScalaTest Matchers DSL" should {
    "provide an and operator," which {
      "returns silently when evaluating true and true" in {}
      "throws a TestFailedException when evaluating true and false" in {}
      "throws a TestFailedException when evaluating false and true" in {}
      "throws a TestFailedException when evaluating false and false" in {}
    }
    "provide an or operator," which {
      "returns silently when evaluating true or true" in {}
      "returns silently when evaluating true or false" in {}
      "returns silently when evaluating false or true" in {}
      "throws a TestFailedException when evaluating false or false" in {}
    }
  }
}

Running the above AndOrSpec in the interpreter would yield:

scala> org.scalatest.run(new AndOrSpec)
AndOrSpec:
The ScalaTest Matchers DSL
  should provide an and operator, which
  - returns silently when evaluating true and true
  - throws a TestFailedException when evaluating true and false
  - throws a TestFailedException when evaluating false and true
  - throws a TestFailedException when evaluating false and false
  should provide an or operator, which
  - returns silently when evaluating true or true
  - returns silently when evaluating true or false
  - returns silently when evaluating false or true
  - throws a TestFailedException when evaluating false or false

Note that unlike when and should/must/can, a which appears in the output right where you put it in the input, at the end of the line, to maximize readability.

If a word or phrase is repeated at the beginning of each string contained in a block, you can eliminate that repetition by using an after word. An after word is a word or phrase that you can place after when, a verb, or which. For example, in the previous WordSpec, the word "provide" is repeated at the beginning of each string inside the should block. You can factor out this duplication like this:

import org.scalatest.WordSpec

class AndOrSpec extends WordSpec {

   def provide = afterWord("provide")

  "The ScalaTest Matchers DSL" should provide {
    "an and operator," which {
      "returns silently when evaluating true and true" in {}
      "throws a TestFailedException when evaluating true and false" in {}
      "that throws a TestFailedException when evaluating false and true" in {}
      "throws a TestFailedException when evaluating false and false" in {}
    }
    "an or operator," which {
      "returns silently when evaluating true or true" in {}
      "returns silently when evaluating true or false" in {}
      "returns silently when evaluating false or true" in {}
      "throws a TestFailedException when evaluating false or false" in {}
    }
  }
}

Running the above version of AndOrSpec with the provide after word in the interpreter would give you:

scala> org.scalatest.run(new AndOrSpec)
AndOrSpec:
The ScalaTest Matchers DSL
  should provide
    an and operator, which
    - returns silently when evaluating true and true
    - throws a TestFailedException when evaluating true and false
    - that throws a TestFailedException when evaluating false and true
    - throws a TestFailedException when evaluating false and false
    an or operator, which
    - returns silently when evaluating true or true
    - returns silently when evaluating true or false
    - returns silently when evaluating false or true
    - throws a TestFailedException when evaluating false or false

Once you've defined an after word, you can place it after when, a verb (should, must, or can), or which. (You can't place one after in or is, the words that introduce a test.) Here's an example that has after words used in all three places:

import org.scalatest.WordSpec

class ScalaTestGUISpec extends WordSpec {

  def theUser = afterWord("the user")
  def display = afterWord("display")
  def is = afterWord("is")

  "The ScalaTest GUI" when theUser {
    "clicks on an event report in the list box" should display {
      "a blue background in the clicked-on row in the list box" in {}
      "the details for the event in the details area" in {}
      "a rerun button," which is {
        "enabled if the clicked-on event is rerunnable" in {}
        "disabled if the clicked-on event is not rerunnable" in {}
      }
    }
  }
}

Running the previous WordSpec in the Scala interpreter would yield:

scala> org.scalatest.run(new ScalaTestGUISpec)
ScalaTestGUISpec:
The ScalaTest GUI
  when the user clicks on an event report in the list box
    should display
    - a blue background in the clicked-on row in the list box
    - the details for the event in the details area
      a rerun button, which is
      - enabled if the clicked-on event is rerunnable
      - disabled if the clicked-on event is not rerunnable

In case when you need to use different verb for a same subject, you can use it or they shorthand to avoid subject duplication:

"A Stack" when {
  // ...
}

it should {
  // ...
}

A WordSpec's lifecycle has two phases: the registration phase and the ready phase. It starts in registration phase and enters ready phase the first time run is called on it. It then remains in ready phase for the remainder of its lifetime.

Tests can only be registered while the WordSpec is in its registration phase. Any attempt to register a test after the WordSpec has entered its ready phase, i.e., after run has been invoked on the WordSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using WordSpec is to register tests during object construction as is done in all the examples shown here. If you keep to the recommended style, you should never see a TestRegistrationClosedException.

Note: Class WordSpec is in part inspired by class org.specs.Specification, designed by Eric Torreborre for the specs framework.

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, WordSpec adds a method ignore to strings that can be used instead of in to register a test. For example, to temporarily disable the test with the name "A Stack should pop values in last-in-first-out order", just change “in” into “ignore,” like this:

package org.scalatest.examples.wordspec.ignore

import org.scalatest.WordSpec

class SetSpec extends WordSpec {

  "A Set" when {
    "empty" should {
      "have size 0" ignore {
        assert(Set.empty.size === 0)
      }

      "produce NoSuchElementException when head is invoked" in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

If you run this version of SetSpec with:

scala> org.scalatest.run(new SetSpec)

It will run only the second test and report that the first test was ignored:

A Set
  when empty
  - should have size 0 !!! IGNORED !!!
  - should should produce NoSuchElementException when head is invoked

If you wish to temporarily ignore an entire suite of tests, you can (on the JVM, not Scala.js) annotate the test class with @Ignore, like this:

package org.scalatest.examples.wordspec.ignoreall

import org.scalatest.WordSpec
import org.scalatest.Ignore

@Ignore
class SetSpec extends WordSpec {

  "A Set" when {
    "empty" should {
      "have size 0" in {
        assert(Set.empty.size === 0)
      }

      "produce NoSuchElementException when head is invoked" in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

When you mark a test class with a tag annotation, ScalaTest will mark each test defined in that class with that tag. Thus, marking the SetSpec in the above example with the @Ignore tag annotation means that both tests in the class will be ignored. If you run the above SetSpec in the Scala interpreter, you'll see:

scala> org.scalatest.run(new SetSpec)
SetSpec:
A Set
  when empty
  - should have size 0 !!! IGNORED !!!
  - should produce NoSuchElementException when head is invoked !!! IGNORED !!!

Note that marking a test class as ignored won't prevent it from being discovered by ScalaTest. Ignored classes will be discovered and run, and all their tests will be reported as ignored. This is intended to keep the ignored class visible, to encourage the developers to eventually fix and “un-ignore” it. If you want to prevent a class from being discovered at all (on the JVM, not Scala.js), use the DoNotDiscover annotation instead.

Informers

One of the parameters to WordSpec's run method is a Reporter, which will collect and report information about the running suite of tests. Information about suites and tests that were run, whether tests succeeded or failed, and tests that were ignored will be passed to the Reporter as the suite runs. Most often the reporting done by default by WordSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event.

One use case for the Informer is to pass more information about a specification to the reporter. For example, the GivenWhenThen trait provides methods that use the implicit info provided by WordSpec to pass such information to the reporter. Here's an example:

package org.scalatest.examples.wordspec.info

import collection.mutable
import org.scalatest._

class SetSpec extends WordSpec with GivenWhenThen {

  "A mutable Set" should {
    "allow an element to be added" in {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      info("That's all folks!")
    }
  }
}

If you run this WordSpec from the interpreter, you will see the following output:

scala> org.scalatest.run(new SetSpec)
A mutable Set
- should allow an element to be added
  + Given an empty mutable Set
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + That's all folks!

Documenters

WordSpec also provides a markup method that returns a Documenter, which allows you to send to the Reporter text formatted in Markdown syntax. You can pass the extra information to the Documenter via its apply method. The Documenter will then pass the information to the Reporter via an MarkupProvided event.

Here's an example WordSpec that uses markup:

package org.scalatest.examples.wordspec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends WordSpec with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

To implement a concrete mutable set, you need to provide implementations
of the following methods:

    def contains(elem: A): Boolean
    def iterator: Iterator[A]
    def += (elem: A): this.type
    def -= (elem: A): this.type

If you wish that methods like `take`,
`drop`, `filter` return the same kind of set,
you should also override:

    def empty: This

It is also good idea to override methods `foreach` and
`size` for efficiency.

  """ }

  "A mutable Set" should {
    "allow an element to be added" in {
      Given("an empty mutable Set")
      val set = mutable.Set.empty[String]

      When("an element is added")
      set += "clarity"

      Then("the Set should have size 1")
      assert(set.size === 1)

      And("the Set should contain the added element")
      assert(set.contains("clarity"))

      markup("This test finished with a **bold** statement!")
    }
  }
}

Although all of ScalaTest's built-in reporters will display the markup text in some form, the HTML reporter will format the markup information into HTML. Thus, the main purpose of markup is to add nicely formatted text to HTML reports. Here's what the above SetSpec would look like in the HTML reporter:

Notifiers and alerters

ScalaTest records text passed to info and markup during tests, and sends the recorded text in the recordedEvents field of test completion events like TestSucceeded and TestFailed. This allows string reporters (like the standard out reporter) to show info and markup text after the test name in a color determined by the outcome of the test. For example, if the test fails, string reporters will show the info and markup text in red. If a test succeeds, string reporters will show the info and markup text in green. While this approach helps the readability of reports, it means that you can't use info to get status updates from long running tests.

To get immediate (i.e., non-recorded) notifications from tests, you can use note (a Notifier) and alert (an Alerter). Here's an example showing the differences:

package org.scalatest.examples.wordspec.note

import collection.mutable
import org.scalatest._

class SetSpec extends WordSpec {

  "A mutable Set" should {
    "allow an element to be added" in {

      info("info is recorded")
      markup("markup is *also* recorded")
      note("notes are sent immediately")
      alert("alerts are also sent immediately")

      val set = mutable.Set.empty[String]
      set += "clarity"
      assert(set.size === 1)
      assert(set.contains("clarity"))
    }
  }
}

Because note and alert information is sent immediately, it will appear before the test name in string reporters, and its color will be unrelated to the ultimate outcome of the test: note text will always appear in green, alert text will always appear in yellow. Here's an example:

scala> org.scalatest.run(new SetSpec)
SetSpec:
A mutable Set
  + notes are sent immediately
  + alerts are also sent immediately
- should allow an element to be added
  + info is recorded
  + markup is *also* recorded

Another example is slowpoke notifications. If you find a test is taking a long time to complete, but you're not sure which test, you can enable slowpoke notifications. ScalaTest will use an Alerter to fire an event whenever a test has been running longer than a specified amount of time.

In summary, use info and markup for text that should form part of the specification output. Use note and alert to send status notifications. (Because the HTML reporter is intended to produce a readable, printable specification, info and markup text will appear in the HTML report, but note and alert text will not.)

Pending tests

A pending test is one that has been given a name but is not yet implemented. The purpose of pending tests is to facilitate a style of testing in which documentation of behavior is sketched out before tests are written to verify that behavior (and often, before the behavior of the system being tested is itself implemented). Such sketches form a kind of specification of what tests and functionality to implement later.

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. The test can also include some code that sends more information about the behavior to the reporter when the tests run. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (In other words, the code of a pending test is executed just like any other test.) However, because the test completes abruptly with TestPendingException, the test will be reported as pending, to indicate the actual test, and possibly the functionality it is intended to test, has not yet been implemented. You can mark tests as pending in a WordSpec like this:

package org.scalatest.examples.wordspec.pending

import org.scalatest._

class SetSpec extends WordSpec {

  "A Set" when {
    "empty" should {
      "have size 0" in (pending)

      "produce NoSuchElementException when head is invoked" in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

If you run this version of SetSpec with:

scala> org.scalatest.run(new SetSpec)

It will run both tests but report that should have size 0 is pending. You'll see:

A Set
  when empty
  - should have size 0 (pending)
  - should produce NoSuchElementException when head is invoked

One difference between an ignored test and a pending one is that an ignored test is intended to be used during a significant refactorings of the code under test, when tests break and you don't want to spend the time to fix all of them immediately. You can mark some of those broken tests as ignored temporarily, so that you can focus the red bar on just failing tests you actually want to fix immediately. Later you can go back and fix the ignored tests. In other words, by ignoring some failing tests temporarily, you can more easily notice failed tests that you actually want to fix. By contrast, a pending test is intended to be used before a test and/or the code under test is written. Pending indicates you've decided to write a test for a bit of behavior, but either you haven't written the test yet, or have only written part of it, or perhaps you've written the test but don't want to implement the behavior it tests until after you've implemented a different bit of behavior you realized you need first. Thus ignored tests are designed to facilitate refactoring of existing code whereas pending tests are designed to facilitate the creation of new code.

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException. The reason for this difference is that it enables your unfinished test to send InfoProvided messages to the reporter before it completes abruptly with TestPendingException, as shown in the previous example on Informers that used the GivenWhenThen trait. For example, the following snippet in a WordSpec:

"The Scala language" should {
   "add correctly" in {
     Given("two integers")
     When("they are added")
     Then("the result is the sum of the two numbers")
     pending
   }
   // ...

Would yield the following output when run in the interpreter:

The Scala language
- should add correctly (pending)
  + Given two integers
  + When they are added
  + Then the result is the sum of the two numbers

Tagging tests

A WordSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing a WordSpec, groups of tests can optionally be included and/or excluded. To tag a WordSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified name, com.mycompany.tags.DbTest, then you could create a matching tag for WordSpecs like this:

package org.scalatest.examples.wordspec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place WordSpec tests into groups with tags like this:

import org.scalatest.WordSpec
import org.scalatest.tagobjects.Slow

class SetSpec extends WordSpec {

  "A Set" when {
    "empty" should {
      "have size 0" taggedAs(Slow) in {
        assert(Set.empty.size === 0)
      }

      "produce NoSuchElementException when head is invoked" taggedAs(Slow, DbTest) in {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

The run method takes a Filter, whose constructor takes an optional Set[String] called tagsToInclude and a Set[String] called tagsToExclude. If tagsToInclude is None, all tests will be run except those those belonging to tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests belonging to tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

It is recommended, though not required, that you create a corresponding tag annotation when you create a Tag object. A tag annotation (on the JVM, not Scala.js) allows you to tag all the tests of a WordSpec in one stroke by annotating the class. For more information and examples, see the documentation for class Tag. On Scala.js, to tag all tests of a suite, you'll need to tag each test individually at the test site.

Shared fixtures

A test fixture is composed of the objects and other artifacts (files, sockets, database connections, etc.) tests use to do their work. When multiple tests need to work with the same fixtures, it is important to try and avoid duplicating the fixture code across those tests. The more code duplication you have in your tests, the greater drag the tests will have on refactoring the actual production code.

ScalaTest recommends three techniques to eliminate such code duplication:

Refactor using Scala
Override withFixture
Mix in a before-and-after trait

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and more amenable for parallel test execution.

The following sections describe these techniques, including explaining the recommended usage for each. But first, here's a table summarizing the options:

Refactor using Scala when different tests need different fixtures.
get-fixture methods	The extract method refactor helps you create a fresh instances of mutable fixture objects in each test that needs them, but doesn't help you clean them up when you're done.
fixture-context objects	By placing fixture methods and fields into traits, you can easily give each test just the newly created fixtures it needs by mixing together traits. Use this technique when you need different combinations of mutable fixture objects in different tests, and don't need to clean up after.
loan-fixture methods	Factor out dupicate code with the loan pattern when different tests need different fixtures that must be cleaned up afterwards.
Override `withFixture` when most or all tests need the same fixture.
`withFixture(NoArgTest)`	The recommended default approach when most or all tests need the same fixture treatment. This general technique allows you, for example, to perform side effects at the beginning and end of all or most tests, transform the outcome of tests, retry tests, make decisions based on test names, tags, or other test data. Use this technique unless: Different tests need different fixtures (refactor using Scala instead) An exception in fixture code should abort the suite, not fail the test (use a before-and-after trait instead) You have objects to pass into tests (override `withFixture(OneArgTest)` instead)
`withFixture(OneArgTest)`	Use when you want to pass the same fixture object or objects as a parameter into all or most tests.
Mix in a before-and-after trait when you want an aborted suite, not a failed test, if the fixture code fails.
`BeforeAndAfter`	Use this boilerplate-buster when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.
`BeforeAndAfterEach`	Use when you want to stack traits that perform the same side-effects before and/or after tests, rather than at the beginning or end of tests.

Calling get-fixture methods

If you need to create the same mutable fixture objects in multiple tests, and don't need to clean them up after using them, the simplest approach is to write one or more get-fixture methods. A get-fixture method returns a new instance of a needed fixture object (or an holder object containing multiple fixture objects) each time it is called. You can call a get-fixture method at the beginning of each test that needs the fixture, storing the returned object or objects in local variables. Here's an example:

package org.scalatest.examples.wordspec.getfixture

import org.scalatest.WordSpec
import collection.mutable.ListBuffer

class ExampleSpec extends WordSpec {

  class Fixture {
    val builder = new StringBuilder("ScalaTest is ")
    val buffer = new ListBuffer[String]
  }

  def fixture = new Fixture

  "Testing" should {
    "be easy" in {
      val f = fixture
      f.builder.append("easy!")
      assert(f.builder.toString === "ScalaTest is easy!")
      assert(f.buffer.isEmpty)
      f.buffer += "sweet"
    }

    "be fun" in {
      val f = fixture
      f.builder.append("fun!")
      assert(f.builder.toString === "ScalaTest is fun!")
      assert(f.buffer.isEmpty)
    }
  }
}

The “f.” in front of each use of a fixture object provides a visual indication of which objects are part of the fixture, but if you prefer, you can import the the members with “import f._” and use the names directly.

If you need to configure fixture objects differently in different tests, you can pass configuration into the get-fixture method. For example, you could pass in an initial value for a mutable fixture object as a parameter to the get-fixture method.

Instantiating fixture-context objects

An alternate technique that is especially useful when different tests need different combinations of fixture objects is to define the fixture objects as instance variables of fixture-context objects whose instantiation forms the body of tests. Like get-fixture methods, fixture-context objects are only appropriate if you don't need to clean up the fixtures after using them.

To use this technique, you define instance variables intialized with fixture objects in traits and/or classes, then in each test instantiate an object that contains just the fixture objects needed by the test. Traits allow you to mix together just the fixture objects needed by each test, whereas classes allow you to pass data in via a constructor to configure the fixture objects. Here's an example in which fixture objects are partitioned into two traits and each test just mixes together the traits it needs:

package org.scalatest.examples.wordspec.fixturecontext

import collection.mutable.ListBuffer
import org.scalatest.WordSpec

class ExampleSpec extends WordSpec {

  trait Builder {
    val builder = new StringBuilder("ScalaTest is ")
  }

  trait Buffer {
    val buffer = ListBuffer("ScalaTest", "is")
  }

  "Testing" should {
    // This test needs the StringBuilder fixture
    "be productive" in new Builder {
      builder.append("productive!")
      assert(builder.toString === "ScalaTest is productive!")
    }
  }

  "Test code" should {
    // This test needs the ListBuffer[String] fixture
    "be readable" in new Buffer {
      buffer += ("readable!")
      assert(buffer === List("ScalaTest", "is", "readable!"))
    }

    // This test needs both the StringBuilder and ListBuffer
    "be clear and concise" in new Builder with Buffer {
      builder.append("clear!")
      buffer += ("concise!")
      assert(builder.toString === "ScalaTest is clear!")
      assert(buffer === List("ScalaTest", "is", "concise!"))
    }
  }
}

Overriding `withFixture(NoArgTest)`

Although the get-fixture method and fixture-context object approaches take care of setting up a fixture at the beginning of each test, they don't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgTest), one of ScalaTest's lifecycle methods defined in trait Suite.

Trait Suite's implementation of runTest passes a no-arg test function to withFixture(NoArgTest). It is withFixture's responsibility to invoke that test function. Suite's implementation of withFixture simply invokes the function, like this:

// Default implementation in trait Suite
protected def withFixture(test: NoArgTest) = {
  test()
}

You can, therefore, override withFixture to perform setup before and/or cleanup after invoking the test function. If you have cleanup to perform, you should invoke the test function inside a try block and perform the cleanup in a finally clause, in case an exception propagates back through withFixture. (If a test fails because of an exception, the test function invoked by withFixture will result in a Failed wrapping the exception. Nevertheless, best practice is to perform cleanup in a finally clause just in case an exception occurs.)

The withFixture method is designed to be stacked, and to enable this, you should always call the super implementation of withFixture, and let it invoke the test function rather than invoking the test function directly. Instead of writing “test()”, you should write “super.withFixture(test)”, like this:

// Your implementation
override def withFixture(test: NoArgTest) = {
  // Perform setup
  try super.withFixture(test) // Invoke the test function
  finally {
    // Perform cleanup
  }
}

Here's an example in which withFixture(NoArgTest) is used to take a snapshot of the working directory if a test fails, and send that information to the reporter:

package org.scalatest.examples.wordspec.noargtest

import java.io.File
import org.scalatest._

class ExampleSpec extends WordSpec {

  override def withFixture(test: NoArgTest) = {

    super.withFixture(test) match {
      case failed: Failed =>
        val currDir = new File(".")
        val fileNames = currDir.list()
        info("Dir snapshot: " + fileNames.mkString(", "))
        failed
      case other => other
    }
  }

  "This test" should {
    "succeed" in {
      assert(1 + 1 === 2)
    }

    "fail" in {
      assert(1 + 1 === 3)
    }
  }
}

Running this version of ExampleSuite in the interpreter in a directory with two files, hello.txt and world.txt would give the following output:

scala> org.scalatest.run(new ExampleSuite)
ExampleSuite:
This test
- should succeed
- should fail *** FAILED ***
  2 did not equal 3 (:33)
  + Dir snapshot: hello.txt, world.txt

Note that the NoArgTest passed to withFixture, in addition to an apply method that executes the test, also includes the test name and the config map passed to runTest. Thus you can also use the test name and configuration objects in your withFixture implementation.

Calling loan-fixture methods

If you need to both pass a fixture object into a test and perform cleanup at the end of the test, you'll need to use the loan pattern. If different tests need different fixtures that require cleanup, you can implement the loan pattern directly by writing loan-fixture methods. A loan-fixture method takes a function whose body forms part or all of a test's code. It creates a fixture, passes it to the test code by invoking the function, then cleans up the fixture after the function returns.

The following example shows three tests that use two fixtures, a database and a file. Both require cleanup after, so each is provided via a loan-fixture method. (In this example, the database is simulated with a StringBuffer.)

import java.util.concurrent.ConcurrentHashMap

object DbServer { // Simulating a database server
  type Db = StringBuffer
  private val databases = new ConcurrentHashMap[String, Db]
  def createDb(name: String): Db = {
    val db = new StringBuffer
    databases.put(name, db)
    db
  }
  def removeDb(name: String) {
    databases.remove(name)
  }
}

import org.scalatest.WordSpec
import DbServer._
import java.util.UUID.randomUUID
import java.io._

class ExampleSpec extends WordSpec {

  def withDatabase(testCode: Db => Any) {
    val dbName = randomUUID.toString
    val db = createDb(dbName) // create the fixture
    try {
      db.append("ScalaTest is ") // perform setup
      testCode(db) // "loan" the fixture to the test
    }
    finally removeDb(dbName) // clean up the fixture
  }

  def withFile(testCode: (File, FileWriter) => Any) {
    val file = File.createTempFile("hello", "world") // create the fixture
    val writer = new FileWriter(file)
    try {
      writer.write("ScalaTest is ") // set up the fixture
      testCode(file, writer) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  "Testing" should {
    // This test needs the file fixture
    "be productive" in withFile { (file, writer) =>
      writer.write("productive!")
      writer.flush()
      assert(file.length === 24)
    }
  }

  "Test code" should {
    // This test needs the database fixture
    "be readable" in withDatabase { db =>
      db.append("readable!")
      assert(db.toString === "ScalaTest is readable!")
    }

    // This test needs both the file and the database
    "be clear and concise" in withDatabase { db =>
      withFile { (file, writer) => // loan-fixture methods compose
        db.append("clear!")
        writer.write("concise!")
        writer.flush()
        assert(db.toString === "ScalaTest is clear!")
        assert(file.length === 21)
      }
    }
  }
}

As demonstrated by the last test, loan-fixture methods compose. Not only do loan-fixture methods allow you to give each test the fixture it needs, they allow you to give a test multiple fixtures and clean everything up afterwards.

Also demonstrated in this example is the technique of giving each test its own "fixture sandbox" to play in. When your fixtures involve external side-effects, like creating files or databases, it is a good idea to give each file or database a unique name as is done in this example. This keeps tests completely isolated, allowing you to run them in parallel if desired.

Overriding `withFixture(OneArgTest)`

If all or most tests need the same fixture, you can avoid some of the boilerplate of the loan-fixture method approach by using a fixture.WordSpec and overriding withFixture(OneArgTest). Each test in a fixture.WordSpec takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgTest. This withFixture method is responsible for invoking the one-arg test function, so you can perform fixture set up before, and clean up after, invoking and passing the fixture into the test function.

To enable the stacking of traits that define withFixture(NoArgTest), it is a good idea to let withFixture(NoArgTest) invoke the test function instead of invoking the test function directly. To do so, you'll need to convert the OneArgTest to a NoArgTest. You can do that by passing the fixture object to the toNoArgTest method of OneArgTest. Instead of writing “test(theFixture)”, you'd delegate responsibility for invoking the test function to the withFixture(NoArgTest) method of the same instance by writing:

withFixture(test.toNoArgTest(theFixture))

Here's a complete example:

package org.scalatest.examples.wordspec.oneargtest

import org.scalatest.fixture
import java.io._

class ExampleSpec extends fixture.WordSpec {

  case class FixtureParam(file: File, writer: FileWriter)

  def withFixture(test: OneArgTest) = {
    val file = File.createTempFile("hello", "world") // create the fixture
    val writer = new FileWriter(file)
    val theFixture = FixtureParam(file, writer)

    try {
      writer.write("ScalaTest is ") // set up the fixture
      withFixture(test.toNoArgTest(theFixture)) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  "Testing" should {
    "be easy" in { f =>
      f.writer.write("easy!")
      f.writer.flush()
      assert(f.file.length === 18)
    }

    "be fun" in { f =>
      f.writer.write("fun!")
      f.writer.flush()
      assert(f.file.length === 17)
    }
  }
}

In this example, the tests actually required two fixture objects, a File and a FileWriter. In such situations you can simply define the FixtureParam type to be a tuple containing the objects, or as is done in this example, a case class containing the objects. For more information on the withFixture(OneArgTest) technique, see the documentation for fixture.WordSpec.

Mixing in `BeforeAndAfter`

In all the shared fixture examples shown so far, the activities of creating, setting up, and cleaning up the fixture objects have been performed during the test. This means that if an exception occurs during any of these activities, it will be reported as a test failure. Sometimes, however, you may want setup to happen before the test starts, and cleanup after the test has completed, so that if an exception occurs during setup or cleanup, the entire suite aborts and no more tests are attempted. The simplest way to accomplish this in ScalaTest is to mix in trait BeforeAndAfter. With this trait you can denote a bit of code to run before each test with before and/or after each test each test with after, like this:

package org.scalatest.examples.wordspec.beforeandafter

import org.scalatest.WordSpec
import org.scalatest.BeforeAndAfter
import collection.mutable.ListBuffer

class ExampleSpec extends WordSpec with BeforeAndAfter {

  val builder = new StringBuilder
  val buffer = new ListBuffer[String]

  before {
    builder.append("ScalaTest is ")
  }

  after {
    builder.clear()
    buffer.clear()
  }

  "Testing" should {
    "be easy" in {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    "be fun" in {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
    }
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class (on the JVM, not Scala.js) unless you synchronized access to the shared, mutable state. This is why ScalaTest's ParallelTestExecution trait extends OneInstancePerTest. By running each test in its own instance of the class, each test has its own copy of the instance variables, so you don't need to synchronize. If you mixed ParallelTestExecution into the ExampleSuite above, the tests would run in parallel just fine without any synchronization needed on the mutable StringBuilder and ListBuffer[String] objects.

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead, as shown later in the next section, composing fixtures by stacking traits.

Composing fixtures by stacking traits

In larger projects, teams often end up with several different fixtures that test classes need in different combinations, and possibly initialized (and cleaned up) in different orders. A good way to accomplish this in ScalaTest is to factor the individual fixtures into traits that can be composed using the stackable trait pattern. This can be done, for example, by placing withFixture methods in several traits, each of which call super.withFixture. Here's an example in which the StringBuilder and ListBuffer[String] fixtures used in the previous examples have been factored out into two stackable fixture traits named Builder and Buffer:

package org.scalatest.examples.wordspec.composingwithfixture

import org.scalatest._
import collection.mutable.ListBuffer

trait Builder extends TestSuiteMixin { this: TestSuite =>

  val builder = new StringBuilder

  abstract override def withFixture(test: NoArgTest) = {
    builder.append("ScalaTest is ")
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally builder.clear()
  }
}

trait Buffer extends TestSuiteMixin { this: TestSuite =>

  val buffer = new ListBuffer[String]

  abstract override def withFixture(test: NoArgTest) = {
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally buffer.clear()
  }
}

class ExampleSpec extends WordSpec with Builder with Buffer {

  "Testing" should {
    "be easy" in {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    "be fun" in {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }
  }
}

By mixing in both the Builder and Buffer traits, ExampleSpec gets both fixtures, which will be initialized before each test and cleaned up after. The order the traits are mixed together determines the order of execution. In this case, Builder is “super” to Buffer. If you wanted Buffer to be “super” to Builder, you need only switch the order you mix them together, like this:

class Example2Spec extends WordSpec with Buffer with Builder

And if you only need one fixture you mix in only that trait:

class Example3Spec extends WordSpec with Builder

Another way to create stackable fixture traits is by extending the BeforeAndAfterEach and/or BeforeAndAfterAll traits. BeforeAndAfterEach has a beforeEach method that will be run before each test (like JUnit's setUp), and an afterEach method that will be run after (like JUnit's tearDown). Similarly, BeforeAndAfterAll has a beforeAll method that will be run before all tests, and an afterAll method that will be run after all tests. Here's what the previously shown example would look like if it were rewritten to use the BeforeAndAfterEach methods instead of withFixture:

package org.scalatest.examples.wordspec.composingbeforeandaftereach

import org.scalatest._
import org.scalatest.BeforeAndAfterEach
import collection.mutable.ListBuffer

trait Builder extends BeforeAndAfterEach { this: Suite =>

  val builder = new StringBuilder

  override def beforeEach() {
    builder.append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builder.clear()
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  val buffer = new ListBuffer[String]

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally buffer.clear()
  }
}

class ExampleSpec extends WordSpec with Builder with Buffer {

  "Testing" should {
    "be easy" in {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    "be fun" in {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }
  }
}

To get the same ordering as withFixture, place your super.beforeEach call at the end of each beforeEach method, and the super.afterEach call at the beginning of each afterEach method, as shown in the previous example. It is a good idea to invoke super.afterEach in a try block and perform cleanup in a finally clause, as shown in the previous example, because this ensures the cleanup code is performed even if super.afterEach throws an exception.

The difference between stacking traits that extend BeforeAndAfterEach versus traits that implement withFixture is that setup and cleanup code happens before and after the test in BeforeAndAfterEach, but at the beginning and end of the test in withFixture. Thus if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the beforeEach or afterEach methods of BeforeAndAfterEach complete abruptly, it is considered an aborted suite, which will result in a SuiteAborted event.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. In other words, you may want to write tests that are "shared" by different fixture objects. To accomplish this in a WordSpec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any WordSpec that uses them, so that the tests they contain will be registered as tests in that WordSpec. For example, given this stack class:

import scala.collection.mutable.ListBuffer

class Stack[T] {

  val MAX = 10
  private val buf = new ListBuffer[T]

  def push(o: T) {
    if (!full)
      buf.prepend(o)
    else
      throw new IllegalStateException("can't push onto a full stack")
  }

  def pop(): T = {
    if (!empty)
      buf.remove(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def peek: T = {
    if (!empty)
      buf(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def full: Boolean = buf.size == MAX
  def empty: Boolean = buf.size == 0
  def size = buf.size

  override def toString = buf.mkString("Stack(", ", ", ")")
}

You may want to test the Stack class in different states: empty, full, with one item, with one item less than capacity, etc. You may find you have several tests that make sense any time the stack is non-empty. Thus you'd ideally want to run those same tests for three stack fixture objects: a full stack, a stack with a one item, and a stack with one item less than capacity. With shared tests, you can factor these tests out into a behavior function, into which you pass the stack fixture to use when running the tests. So in your WordSpec for stack, you'd invoke the behavior function three times, passing in each of the three stack fixtures so that the shared tests are run for all three fixtures. You can define a behavior function that encapsulates these shared tests inside the WordSpec that uses them. If they are shared between different WordSpecs, however, you could also define them in a separate trait that is mixed into each WordSpec that uses them.

For example, here the nonEmptyStack behavior function (in this case, a behavior method) is defined in a trait along with another method containing shared tests for non-full stacks:

trait StackBehaviors { this: WordSpec =>

  def nonEmptyStack(newStack: => Stack[Int], lastItemAdded: Int) {

    "be non-empty" in {
      assert(!newStack.empty)
    }

    "return the top item on peek" in {
      assert(newStack.peek === lastItemAdded)
    }

    "not remove the top item on peek" in {
      val stack = newStack
      val size = stack.size
      assert(stack.peek === lastItemAdded)
      assert(stack.size === size)
    }

    "remove the top item on pop" in {
      val stack = newStack
      val size = stack.size
      assert(stack.pop === lastItemAdded)
      assert(stack.size === size - 1)
    }
  }

  def nonFullStack(newStack: => Stack[Int]) {

    "not be full" in {
      assert(!newStack.full)
    }

    "add to the top on push" in {
      val stack = newStack
      val size = stack.size
      stack.push(7)
      assert(stack.size === size + 1)
      assert(stack.peek === 7)
    }
  }
}

Given these behavior functions, you could invoke them directly, but WordSpec offers a DSL for the purpose, which looks like this:

behave like nonEmptyStack(stackWithOneItem, lastValuePushed)
behave like nonFullStack(stackWithOneItem)

If you prefer to use an imperative style to change fixtures, for example by mixing in BeforeAndAfterEach and reassigning a stack var in beforeEach, you could write your behavior functions in the context of that var, which means you wouldn't need to pass in the stack fixture because it would be in scope already inside the behavior function. In that case, your code would look like this:

behave like nonEmptyStack // assuming lastValuePushed is also in scope inside nonEmptyStack
behave like nonFullStack

The recommended style, however, is the functional, pass-all-the-needed-values-in style. Here's an example:

class SharedTestExampleSpec extends WordSpec with StackBehaviors {

  // Stack fixture creation methods
  def emptyStack = new Stack[Int]

  def fullStack = {
    val stack = new Stack[Int]
    for (i <- 0 until stack.MAX)
      stack.push(i)
    stack
  }

  def stackWithOneItem = {
    val stack = new Stack[Int]
    stack.push(9)
    stack
  }

  def stackWithOneItemLessThanCapacity = {
    val stack = new Stack[Int]
    for (i <- 1 to 9)
      stack.push(i)
    stack
  }

  val lastValuePushed = 9

  "A Stack" when {
    "empty" should {
      "be empty" in {
        assert(emptyStack.empty)
      }

      "complain on peek" in {
        assertThrows[IllegalStateException] {
          emptyStack.peek
        }
      }

      "complain on pop" in {
        assertThrows[IllegalStateException] {
          emptyStack.pop
        }
      }
    }

    "it contains one item" should {
      behave like nonEmptyStack(stackWithOneItem, lastValuePushed)
      behave like nonFullStack(stackWithOneItem)
    }

    "it contains one item less than capacity" should {
      behave like nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed)
      behave like nonFullStack(stackWithOneItemLessThanCapacity)
    }

    "full" should {
      "be full" in {
        assert(fullStack.full)
      }

      behave like nonEmptyStack(fullStack, lastValuePushed)

      "complain on a push" in {
        assertThrows[IllegalStateException] {
          fullStack.push(10)
        }
      }
    }
  }
}

If you load these classes into the Scala interpreter (with scalatest's JAR file on the class path), and execute it, you'll see:

scala> org.scalatest.run(new SharedTestExampleSpec)
SharedTestExampleSpec:
A Stack
  when empty
  - should be empty
  - should complain on peek
  - should complain on pop
  when it contains one item
  - should be non-empty
  - should return the top item on peek
  - should not remove the top item on peek
  - should remove the top item on pop
  - should not be full
  - should add to the top on push
  when it contains one item less than capacity
  - should be non-empty
  - should return the top item on peek
  - should not remove the top item on peek
  - should remove the top item on pop
  - should not be full
  - should add to the top on push
  when full
  - should be full
  - should be non-empty
  - should return the top item on peek
  - should not remove the top item on peek
  - should remove the top item on pop
  - should complain on a push

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. A good way to solve this problem in a WordSpec is to make sure each invocation of a behavior function is in the context of a different surrounding when, should/must/can, or which clause, because a test's name is the concatenation of its surrounding clauses and after words, followed by the "spec text". For example, the following code in a WordSpec would register a test with the name "A Stack when empty should be empty":

"A Stack" when {
  "empty" should {
    "be empty" in {
      assert(emptyStack.empty)
    }
  }
}
// ...

If the "be empty" test was factored out into a behavior function, it could be called repeatedly so long as each invocation of the behavior function is in the context of a different surrounding when clauses.

trait WordSpecLike extends TestSuite with TestRegistration with ShouldVerb with MustVerb with CanVerb with Informing with Notifying with Alerting with Documenting

Implementation trait for class WordSpec, which facilitates a “behavior-driven” style of development (BDD), in which tests are combined with text that specifies the behavior the tests verify.

WordSpec is a class, not a trait, to minimize compile time given there is a slight compiler overhead to mixing in traits compared to extending classes. If you need to mix the behavior of WordSpec into some other class, you can use this trait instead, because class WordSpec does nothing more than extend this trait and add a nice toString implementation.

See the documentation of the class for a detailed overview of WordSpec.

trait WrapWith extends Annotation

Annotation to associate a wrapper suite with a non-Suite class, so it can be run via ScalaTest.

Note: This is actually an annotation defined in Java, not a Scala trait. It must be defined in Java instead of Scala so it will be accessible at runtime. It has been inserted into Scaladoc by pretending it is a trait.

A class will be considered annotated with WrapWith if it is annotated directly or one of its superclasses (but not supertraits) are annotated with WrapWith. The wrapper suite must have a public, one-arg constructor that takes a Class instance whose type parameter is compatible with the class to wrap: i.e., the class being annotated with WrapWith. ScalaTest will load the class to wrap and construct a new instance of the wrapper suite, passing in the Class instance for the class to wrap. Here's an example:

import org.scalacheck.Properties

@WrapWith(classOf[ScalaCheckPropertiesSpec])
class StringSpecification extends Properties("String") {
  // ...
}

The ScalaCheckPropertiesSpec would need to have a public, no-arg constructor that accepts subclasses of org.scalacheck.Properties:

import org.scalacheck.Properties
import org.scalatest.Suite

class ScalaCheckPropertiesSpec(clazz: Class[_ <: Properties]) extends Suite {
  // ...
}

type PendingNothing = PendingStatement

Annotations: @deprecated
Deprecated: Please use PendingStatement instead

trait Rerunner extends AnyRef

Trait whose instances can rerun tests or other entities (such as suites).

Trait whose instances can rerun tests or other entities (such as suites). An object extending this trait can be passed to a Reporter as part of a Report. The test or other entity about which the report is made can then be rerun by invoking the rerun method on the Rerunnable.

Annotations: @deprecated
Deprecated: We are considering removing Rerunner in ScalaTest 2.0 and would like to know if anyone is using it. If you are, please email scalatest-users@googlegroups.com or and describe your use case. Thanks!

type Spec = RefSpec

The name org.scalatest.Spec has been deprecated and will be removed in a future version of ScalaTest. Please use its new name, org.scalatest.refspec.RefSpec, instead.

Because this style uses reflection at runtime to discover scopes and tests, it can only be supported on the JVM, not Scala.js. Thus in ScalaTest 3.0.0, class org.scalatest.Spec was moved to the org.scalatest.refspec package and renamed RefSpec, with the intention of later moving it to a separate module available only on the JVM.

Annotations: @deprecated
Deprecated: Please use org.scalatest.refspec.RefSpec instead

type SpecLike = RefSpecLike

The name org.scalatest.SpecLike has been deprecated and will be removed in a future version of ScalaTest. Please use its new name, org.scalatest.refspec.RefSpecLike, instead.

Because this style uses reflection at runtime to discover scopes and tests, it can only be supported on the JVM, not Scala.js. Thus in ScalaTest 3.0.0, class org.scalatest.SpecLike was moved to the org.scalatest.refspec package and renamed RefSpecLike, with the intention of later moving it to a separate module available only on the JVM.

Annotations: @deprecated
Deprecated: Please use org.scalatest.refspec.RefSpecLike instead

Packages

scalatest 

package scalatest

Type Members

Expected results

Forcing failures

Achieving success

Expected exceptions

Checking that a snippet of code does or does not compile

Assumptions

Forcing cancelations

Getting a clue

Asynchronous execution model

Serial and parallel test execution

Futures and expected exceptions

Ignored tests

Informers

Documenters

Notifiers and alerters

Pending tests

Tagging tests

Shared fixtures

Calling get-fixture methods

Overriding withFixture(NoArgAsyncTest)

Calling loan-fixture methods

Overriding withFixture(OneArgTest)

Mixing in BeforeAndAfter

Composing fixtures by stacking traits

Shared tests

Asynchronous execution model

Serial and parallel test execution

Futures and expected exceptions

Ignored tests

Informers

Documenters

Notifiers and alerters

Pending tests

Tagging tests

Shared fixtures

Calling get-fixture methods

Overriding withFixture(NoArgAsyncTest)

Calling loan-fixture methods

Overriding withFixture(OneArgTest)

Mixing in BeforeAndAfter

Composing fixtures by stacking traits

Shared tests

Asynchronous execution model

Serial and parallel test execution

Futures and expected exceptions

Ignored tests

Informers

Documenters

Notifiers and alerters

Pending tests

Tagging tests

Shared fixtures

Calling get-fixture methods

Overriding withFixture(NoArgAsyncTest)

Calling loan-fixture methods

Overriding withFixture(OneArgTest)

Mixing in BeforeAndAfter

Composing fixtures by stacking traits

Shared tests

Asynchronous execution model

Serial and parallel test execution

Futures and expected exceptions

Ignored tests

Informers

Documenters

Notifiers and alerters

Pending tests

Tagging tests

Shared fixtures

Calling get-fixture methods

Overriding withFixture(NoArgAsyncTest)

Calling loan-fixture methods

Overriding withFixture(OneArgTest)

Mixing in BeforeAndAfter

Composing fixtures by stacking traits

Shared tests

scalatest

Overriding `withFixture(NoArgAsyncTest)`

Overriding `withFixture(OneArgTest)`

Mixing in `BeforeAndAfter`

Overriding `withFixture(NoArgAsyncTest)`

Overriding `withFixture(OneArgTest)`

Mixing in `BeforeAndAfter`

Overriding `withFixture(NoArgAsyncTest)`

Overriding `withFixture(OneArgTest)`

Mixing in `BeforeAndAfter`

Overriding `withFixture(NoArgAsyncTest)`

Overriding `withFixture(OneArgTest)`

Mixing in `BeforeAndAfter`

Overriding `withFixture(NoArgAsyncTest)`

Overriding `withFixture(OneArgTest)`

Mixing in `BeforeAndAfter`

Overriding `withFixture(NoArgAsyncTest)`

Overriding `withFixture(OneArgTest)`

Mixing in `BeforeAndAfter`

Overriding `withFixture(NoArgTest)`

Overriding `withFixture(OneArgTest)`

Mixing in `BeforeAndAfter`

Overriding `withFixture(NoArgTest)`

Overriding `withFixture(OneArgTest)`

Mixing in `BeforeAndAfter`