freespec

package freespec

Classes and traits for ScalaTest's FreeSpec style.

This package is released as the scalatest-freespec module.

Source: package.scala

Linear Supertypes

AnyRef, Any

Type Members

class AnyFreeSpec extends AnyFreeSpecLike

Facilitates a “behavior-driven” style of development (BDD), in which tests are nested inside text clauses denoted with the dash operator (-).

AnyFreeSpec is so named because unlike classes such as AnyWordSpec, AnyFlatSpec, and AnyFunSpec, it is enforces no structure on the text. You are free to compose text however you like. (A AnyFreeSpec 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, AnyFreeSpec is a good choice for teams experienced with BDD and able to agree on how to structure the specification text.

Here's an example AnyFreeSpec:

package org.scalatest.examples.freespec

import org.scalatest.freespec.AnyFreeSpec

class SetSpec extends AnyFreeSpec {

  "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 AnyFreeSpec 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" - {
  // ...
}

import org.scalatest.freespec.AnyFreeSpec

class StackSpec extends AnyFreeSpec {
  "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 AnyFreeSpec can also be used to write a specification-style test in languages other than English. For example:

import org.scalatest.freespec.AnyFreeSpec

class ComputerRoomRulesSpec extends AnyFreeSpec {
  "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 AnyFreeSpec'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 AnyFreeSpec is in its registration phase. Any attempt to register a test after the AnyFreeSpec has entered its ready phase, i.e., after run has been invoked on the AnyFreeSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using AnyFreeSpec 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, AnyFreeSpec 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.AnyFreeSpec

class SetSpec extends AnyFreeSpec {

  "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.AnyFreeSpec
import org.scalatest.Ignore

@Ignore
class SetSpec extends AnyFreeSpec {

  "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 AnyFreeSpec'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 AnyFreeSpec'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 AnyFreeSpec 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.AnyFreeSpec 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 AnyFreeSpec 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

AnyFreeSpec 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 AnyFreeSpec that uses markup:

package org.scalatest.examples.freespec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends freespec.AnyFreeSpec 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.AnyFreeSpec {

  "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 AnyFreeSpec like this:

package org.scalatest.examples.freespec.pending

import org.scalatest._

class SetSpec extends freespec.AnyFreeSpec {

  "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 AnyFreeSpec:

"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 AnyFreeSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing a AnyFreeSpec, groups of tests can optionally be included and/or excluded. To tag a AnyFreeSpec'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 AnyFreeSpecs like this:

import org.scalatest.Tag

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

Given these definitions, you could tag AnyFreeSpec 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.AnyFreeSpec
import org.scalatest.tagobjects.Slow

class SetSpec extends AnyFreeSpec {

  "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 AnyFreeSpec 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.AnyFreeSpec
import collection.mutable.ListBuffer

class ExampleSpec extends AnyFreeSpec {

  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.AnyFreeSpec

class ExampleSpec extends AnyFreeSpec {

  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.AnyFreeSpec {

  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.AnyFreeSpec
import DbServer._
import java.util.UUID.randomUUID
import java.io._

class ExampleSpec extends AnyFreeSpec {

  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 FixtureAnyFreeSpec and overriding withFixture(OneArgTest). Each test in a FixtureAnyFreeSpec 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._
import java.io._

class ExampleSpec extends freespec.FixtureAnyFreeSpec {

  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 FixtureAnyFreeSpec.

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.AnyFreeSpec
import org.scalatest.BeforeAndAfter
import collection.mutable.ListBuffer

class ExampleSpec extends AnyFreeSpec 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.AnyFreeSpec 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.AnyFreeSpec with Buffer with Builder

And if you only need one fixture you mix in only that trait:

class Example3Spec extends freespec.AnyFreeSpec 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.AnyFreeSpec 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 AnyFreeSpec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any AnyFreeSpec that uses them, so that the tests they contain will be registered as tests in that AnyFreeSpec. 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 AnyFreeSpec 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 AnyFreeSpec that uses them. If they are shared between different AnyFreeSpecs, however, you could also define them in a separate trait that is mixed into each AnyFreeSpec 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: AnyFreeSpec =>

  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 AnyFreeSpec 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 AnyFreeSpec 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 AnyFreeSpec 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 AnyFreeSpec 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 AnyFreeSpecLike extends TestSuite with TestRegistration with Informing with Notifying with Alerting with Documenting
Implementation trait for class AnyFreeSpec, which facilitates a “behavior-driven” style of development (BDD), in which tests are nested inside text clauses denoted with the dash operator (-).
Implementation trait for class AnyFreeSpec, which facilitates a “behavior-driven” style of development (BDD), in which tests are nested inside text clauses denoted with the dash operator (-).
AnyFreeSpec 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 AnyFreeSpec into some other class, you can use this trait instead, because class AnyFreeSpec does nothing more than extend this trait and add a nice toString implementation.
See the documentation of the class for a detailed overview of AnyFreeSpec.

abstract class AsyncFreeSpec extends AsyncFreeSpecLike

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

Recommended Usage: AsyncFreeSpec is intended to enable users of AnyFreeSpec to write non-blocking asynchronous tests that are consistent with their traditional AnyFreeSpec tests. Note: AsyncFreeSpec is intended for use in special situations where non-blocking asynchronous testing is needed, with class AnyFreeSpec 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.freespec.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 AnyFreeSpec, but with tests having result type Assertion or Future[Assertion]. For more examples of structure, see the documentation for AnyFreeSpec.

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 AnyFreeSpec 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 =
    org.scalatest.concurrent.TestExecutionContext.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 AnyFreeSpec) 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.freespec.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.freespec.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 !!!

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 freespec.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 freespec.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
    }
  }
}

Notifiers and alerters

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 freespec.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

Pending tests

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.

package org.scalatest.examples.asyncfreespec.pending

import org.scalatest.freespec.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.

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.freespec.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.

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

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

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

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.freespec.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.

// 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 freespec.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

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 freespec.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!")
          }
        }
      }
    }
  }
}

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 FixtureAsyncTestSuite and overriding withFixture(OneArgAsyncTest). Each test in a FixtureAsyncTestSuite 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 freespec.FixtureAsyncFreeSpec {

  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 FixtureAsyncFreeSpec.

Mixing in `BeforeAndAfter`

package org.scalatest.examples.asyncfreespec.beforeandafter

import org.scalatest.freespec.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 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.

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 freespec.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 freespec.AsyncFreeSpec with Buffer with Builder

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

class Example3Spec extends freespec.AsyncFreeSpec with Builder

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 freespec.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
      }
    }
  }
}

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.freespec.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 (-).
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 FixtureAnyFreeSpec extends FixtureAnyFreeSpecLike

A sister class to org.scalatest.freespec.AnyFreeSpec that can pass a fixture object into its tests.

Recommended Usage: Use class FixtureAnyFreeSpec in situations for which AnyFreeSpec would be a good choice, when all or most tests need the same fixture objects that must be cleaned up afterwards. Note: FixtureAnyFreeSpec is intended for use in special situations, with class AnyFreeSpec used for general needs. For more insight into where FixtureAnyFreeSpec fits in the big picture, see the withFixture(OneArgTest) subsection of the Shared fixtures section in the documentation for class AnyFreeSpec.

Class FixtureAnyFreeSpec behaves similarly to class org.scalatest.freespec.AnyFreeSpec, except that tests may have a fixture parameter. The type of the fixture parameter is defined by the abstract FixtureParam type, which is a member of this class. This class also has an abstract withFixture method. This withFixture method takes a OneArgTest, which is a nested trait defined as a member of this class. OneArgTest has an apply method that takes a FixtureParam. This apply method is responsible for running a test. This class's runTest method delegates the actual running of each test to withFixture(OneArgTest), passing in the test code to run via the OneArgTest argument. The withFixture(OneArgTest) method (abstract in this class) is responsible for creating the fixture argument and passing it to the test function.

Subclasses of this class must, therefore, do three things differently from a plain old org.scalatest.freespec.AnyFreeSpec:

define the type of the fixture parameter by specifying type FixtureParam
define the withFixture(OneArgTest) method
write tests that take a fixture parameter
(You can also define tests that don't take a fixture parameter.)

If the fixture you want to pass into your tests consists of multiple objects, you will need to combine them into one object to use this class. One good approach to passing multiple fixture objects is to encapsulate them in a case class. Here's an example:

case class FixtureParam(file: File, writer: FileWriter)

withFixture(test.toNoArgTest(theFixture))

Here's a complete example:

package org.scalatest.examples.freespec.oneargtest

import org.scalatest.freespec
import java.io._

class ExampleSpec extends freespec.FixtureAnyFreeSpec {

  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)
    }
  }
}

If a test fails, the OneArgTest function will result in a Failed wrapping the exception describing the failure. To ensure clean up happens even if a test fails, you should invoke the test function from inside a try block and do the cleanup in a finally clause, as shown in the previous example.

Sharing fixtures across classes

If multiple test classes need the same fixture, you can define the FixtureParam and withFixture(OneArgTest) implementations in a trait, then mix that trait into the test classes that need it. For example, if your application requires a database and your integration tests use that database, you will likely have many test classes that need a database fixture. You can create a "database fixture" trait that creates a database with a unique name, passes the connector into the test, then removes the database once the test completes. This is shown in the following example:

package org.scalatest.examples.fixture.freespec.sharing

import java.util.concurrent.ConcurrentHashMap
import org.scalatest.fixture
import DbServer._
import java.util.UUID.randomUUID

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)
  }
}

trait DbFixture { this: FixtureSuite =>

  type FixtureParam = Db

  // Allow clients to populate the database after
  // it is created
  def populateDb(db: Db) {}

  def withFixture(test: OneArgTest) = {
    val dbName = randomUUID.toString
    val db = createDb(dbName) // create the fixture
    try {
      populateDb(db) // setup the fixture
      withFixture(test.toNoArgTest(db)) // "loan" the fixture to the test
    }
    finally removeDb(dbName) // clean up the fixture
  }
}

class ExampleSpec extends FixtureAnyFreeSpec with DbFixture {

  override def populateDb(db: Db) { // setup the fixture
    db.append("ScalaTest is ")
  }

  "Testing" - {
    "should be easy" in { db =>
      db.append("easy!")
      assert(db.toString === "ScalaTest is easy!")
    }

    "should be fun" in { db =>
      db.append("fun!")
      assert(db.toString === "ScalaTest is fun!")
    }
  }

  // This test doesn't need a Db
  "Test code" - {
    "should be clear" in { () =>
      val buf = new StringBuffer
      buf.append("ScalaTest code is ")
      buf.append("clear!")
      assert(buf.toString === "ScalaTest code is clear!")
    }
  }
}

Often when you create fixtures in a trait like DbFixture, you'll still need to enable individual test classes to "setup" a newly created fixture before it gets passed into the tests. A good way to accomplish this is to pass the newly created fixture into a setup method, like populateDb in the previous example, before passing it to the test function. Classes that need to perform such setup can override the method, as does ExampleSpec.

If a test doesn't need the fixture, you can indicate that by providing a no-arg instead of a one-arg function, as is done in the third test in the previous example, “Test code should be clear”. In other words, instead of starting your function literal with something like “db =>”, you'd start it with “() =>”. For such tests, runTest will not invoke withFixture(OneArgTest). It will instead directly invoke withFixture(NoArgTest).

Both examples shown above demonstrate 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 these examples. This keeps tests completely isolated, allowing you to run them in parallel if desired. You could mix ParallelTestExecution into either of these ExampleSpec classes, and the tests would run in parallel just fine.

trait FixtureAnyFreeSpecLike extends FixtureTestSuite with FixtureTestRegistration with Informing with Notifying with Alerting with Documenting
Implementation trait for class FixtureAnyFreeSpec, which is a sister class to org.scalatest.freespec.AnyFreeSpec that can pass a fixture object into its tests.
Implementation trait for class FixtureAnyFreeSpec, which is a sister class to org.scalatest.freespec.AnyFreeSpec that can pass a fixture object into its tests.
FixtureAnyFreeSpec 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 FixtureAnyFreeSpec into some other class, you can use this trait instead, because class FixtureAnyFreeSpec does nothing more than extend this trait and add a nice toString implementation.
See the documentation of the class for a detailed overview of FixtureAnyFreeSpec.

abstract class FixtureAsyncFreeSpec extends FixtureAsyncFreeSpecLike

A sister class to org.scalatest.freespec.AsyncFreeSpec that can pass a fixture object into its tests.

Recommended Usage: Use class FixtureAsyncFunSpec in situations for which AsyncFreeSpec would be a good choice, when all or most tests need the same fixture objects that must be cleaned up afterwards. Note: FixtureAsyncFreeSpec is intended for use in special situations, with class AsyncFreeSpec used for general needs. For more insight into where FixtureAsyncFreeSpec fits in the big picture, see the withFixture(OneArgAsyncTest) subsection of the Shared fixtures section in the documentation for class AsyncFunSpec.

Class FixtureAsyncFreeSpec behaves similarly to class org.scalatest.freespec.AsyncFreeSpec, except that tests may have a fixture parameter. The type of the fixture parameter is defined by the abstract FixtureParam type, which is a member of this class. This class also contains an abstract withFixture method. This withFixture method takes a OneArgAsyncTest, which is a nested trait defined as a member of this class. OneArgAsyncTest has an apply method that takes a FixtureParam. This apply method is responsible for running a test. This class's runTest method delegates the actual running of each test to withFixture(OneArgAsyncTest), passing in the test code to run via the OneArgAsyncTest argument. The withFixture(OneArgAsyncTest) method (abstract in this class) is responsible for creating the fixture argument and passing it to the test function.

Subclasses of this class must, therefore, do three things differently from a plain old org.scalatest.freespec.AsyncFunSpec:

define the type of the fixture parameter by specifying type FixtureParam
define the withFixture(OneArgAsyncTest) method
write tests that take a fixture parameter
(You can also define tests that don't take a fixture parameter.)

case class FixtureParam(file: File, writer: FileWriter)

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 freespec.FixtureAsyncFreeSpec {

  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!")
      }
    }
  }
}

If a test fails, the future returned by the OneArgAsyncTest function will result in an org.scalatest.Failed wrapping the exception describing the failure. To ensure clean up happens even if a test fails, you should invoke the test function and do the cleanup using complete-lastly, as shown in the previous example. The complete-lastly syntax, defined in CompleteLastly, which is extended by AsyncTestSuite, ensures the second, cleanup block of code is executed, whether the the first block throws an exception or returns a future. If it returns a future, the cleanup will be executed when the future completes.

Sharing fixtures across classes

If multiple test classes need the same fixture, you can define the FixtureParam and withFixture(OneArgAsyncTest) implementations in a trait, then mix that trait into the test classes that need it. For example, if your application requires a database and your integration tests use that database, you will likely have many test classes that need a database fixture. You can create a "database fixture" trait that creates a database with a unique name, passes the connector into the test, then removes the database once the test completes. This is shown in the following example:

package org.scalatest.examples.fixture.asyncfreespec.sharing

import java.util.concurrent.ConcurrentHashMap
import org.scalatest._
import DbServer._
import java.util.UUID.randomUUID
import scala.concurrent.Future

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)
  }
}

trait DbFixture { this: FixtureAsyncTestSuite =>

  type FixtureParam = Db

  // Allow clients to populate the database after
  // it is created
  def populateDb(db: Db) {}

  def withFixture(test: OneArgAsyncTest): FutureOutcome = {
    val dbName = randomUUID.toString
    val db = createDb(dbName) // create the fixture
    complete {
      populateDb(db) // setup the fixture
      withFixture(test.toNoArgAsyncTest(db)) // "loan" the fixture to the test
    } lastly {
      removeDb(dbName) // ensure the fixture will be cleaned up
    }
  }
}

class ExampleSpec extends freespec.FixtureAsyncFreeSpec with DbFixture {

  override def populateDb(db: Db) { // setup the fixture
    db.append("ScalaTest is ")
  }

 "Testing" - {
    "should be easy" in { db =>
      Future {
        db.append("easy!")
        assert(db.toString === "ScalaTest is easy!")
      }
    }

    "should be fun" in { db =>
      Future {
        db.append("fun!")
        assert(db.toString === "ScalaTest is fun!")
      }
    }

    // This test doesn't need a Db
    "code should be clear" in { () =>
      Future {
        val buf = new StringBuffer
        buf.append("ScalaTest code is ")
        buf.append("clear!")
        assert(buf.toString === "ScalaTest code is clear!")
      }
    }
  }
}

If a test doesn't need the fixture, you can indicate that by providing a no-arg instead of a one-arg function, as is done in the third test in the previous example, “test code should be clear”. In other words, instead of starting your function literal with something like “db =>”, you'd start it with “() =>”. For such tests, runTest will not invoke withFixture(OneArgAsyncTest). It will instead directly invoke withFixture(NoArgAsyncTest).

Both examples shown above demonstrate 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 these examples. This keeps tests completely isolated, allowing you to run them in parallel if desired. You could mix ParallelTestExecution into either of these ExampleSuite classes, and the tests would run in parallel just fine.

trait FixtureAsyncFreeSpecLike extends FixtureAsyncTestSuite with FixtureAsyncTestRegistration with Informing with Notifying with Alerting with Documenting
Implementation trait for class FixtureAsyncFreeSpec, which is a sister class to org.scalatest.freespec.AsyncFreeSpec that can pass a fixture object into its tests.
Implementation trait for class FixtureAsyncFreeSpec, which is a sister class to org.scalatest.freespec.AsyncFreeSpec that can pass a fixture object into its tests.
FixtureAsyncFreeSpec 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 FixtureAsyncFreeSpec into some other class, you can use this trait instead, because class FixtureAsyncFreeSpec does nothing more than extend this trait and add a nice toString implementation.
See the documentation of the class for a detailed overview of FixtureAsyncFreeSpec.

class PathAnyFreeSpec extends PathAnyFreeSpecLike

A sister class to org.scalatest.freespec.PathAnyFreeSpec that isolates tests by running each test in its own instance of the test class, and for each test, only executing the path leading to that test.

Class PathAnyFreeSpec behaves similarly to class org.scalatest.freespec.AnyFreeSpec, except that tests are isolated based on their path. The purpose of PathAnyFreeSpec is to facilitate writing specification-style tests for mutable objects in a clear, boilerpate-free way. To test mutable objects, you need to mutate them. Using a path class, you can make a statement in text, then implement that statement in code (including mutating state), and nest and combine these test/code pairs in any way you wish. Each test will only see the side effects of code that is in blocks that enclose the test. Here's an example:

import org.scalatest.freespec
import org.scalatest.matchers.should.Matchers
import scala.collection.mutable.ListBuffer

class ExampleSpec extends freespec.PathAnyFreeSpec with Matchers {

  "A ListBuffer" - {

    val buf = ListBuffer.empty[Int] // This implements "A ListBuffer"

    "should be empty when created" in {

      // This test sees:
      //   val buf = ListBuffer.empty[Int]
      // So buf is: ListBuffer()

      buf should be ('empty)
    }

    "when 1 is appended" - {

      buf += 1 // This implements "when 1 is appended", etc...

      "should contain 1" in {

        // This test sees:
        //   val buf = ListBuffer.empty[Int]
        //   buf += 1
        // So buf is: ListBuffer(1)

        buf.remove(0) should equal (1)
        buf should be ('empty)
      }

      "when 2 is appended" - {

        buf += 2

        "should contain 1 and 2" in {

          // This test sees:
          //   val buf = ListBuffer.empty[Int]
          //   buf += 1
          //   buf += 2
          // So buf is: ListBuffer(1, 2)

          buf.remove(0) should equal (1)
          buf.remove(0) should equal (2)
          buf should be ('empty)
        }

        "when 2 is removed" - {

          buf -= 2

          "should contain only 1 again" in {

            // This test sees:
            //   val buf = ListBuffer.empty[Int]
            //   buf += 1
            //   buf += 2
            //   buf -= 2
            // So buf is: ListBuffer(1)

            buf.remove(0) should equal (1)
            buf should be ('empty)
          }
        }

        "when 3 is appended" - {

          buf += 3

          "should contain 1, 2, and 3" in {

            // This test sees:
            //   val buf = ListBuffer.empty[Int]
            //   buf += 1
            //   buf += 2
            //   buf += 3
            // So buf is: ListBuffer(1, 2, 3)

            buf.remove(0) should equal (1)
            buf.remove(0) should equal (2)
            buf.remove(0) should equal (3)
            buf should be ('empty)
          }
        }
      }

      "when 88 is appended" - {

        buf += 88

        "should contain 1 and 88" in {

          // This test sees:
          //   val buf = ListBuffer.empty[Int]
          //   buf += 1
          //   buf += 88
          // So buf is: ListBuffer(1, 88)

          buf.remove(0) should equal (1)
          buf.remove(0) should equal (88)
          buf should be ('empty)
        }
      }
    }

    "should have size 0 when created" in {

      // This test sees:
      //   val buf = ListBuffer.empty[Int]
      // So buf is: ListBuffer()

      buf should have size 0
    }
  }
}

Note that the above class is organized by writing a bit of specification text that opens a new block followed by, at the top of the new block, some code that "implements" or "performs" what is described in the text. This is repeated as the mutable object (here, a ListBuffer), is prepared for the enclosed tests. For example:

"A ListBuffer" - {
  val buf = ListBuffer.empty[Int]

Or:

"when 2 is appended" - {
  buf += 2

Note also that although each test mutates the ListBuffer, none of the other tests observe those side effects:

"should contain 1" in {

  buf.remove(0) should equal (1)
  // ...
}

"when 2 is appended" - {

  buf += 2

  "should contain 1 and 2" in {

    // This test does not see the buf.remove(0) from the previous test,
    // so the first element in the ListBuffer is again 1
    buf.remove(0) should equal (1)
    buf.remove(0) should equal (2)

This kind of isolation of tests from each other is a consequence of running each test in its own instance of the test class, and can also be achieved by simply mixing OneInstancePerTest into a regular org.scalatest.freespec.PathAnyFreeSpec. However, PathAnyFreeSpec takes isolation one step further: a test in a PathAnyFreeSpec does not observe side effects performed outside tests in earlier blocks that do not enclose it. Here's an example:

"when 2 is removed" - {

  buf -= 2

  // ...
}

"when 3 is appended" - {

  buf += 3

  "should contain 1, 2, and 3" in {

    // This test does not see the buf -= 2 from the earlier "when 2 is removed" block,
    // because that block does not enclose this test, so the second element in the
    // ListBuffer is still 2
    buf.remove(0) should equal (1)
    buf.remove(0) should equal (2)
    buf.remove(0) should equal (3)

Running the full ExampleSpec, shown above, in the Scala interpeter would give you:

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

scala> run(new ExampleSpec)
ExampleSpec:
A ListBuffer
- should be empty when created
  when 1 is appended
  - should contain 1
    when 2 is appended
    - should contain 1 and 2
      when 2 is removed
      - should contain only 1 again
      when 3 is appended
      - should contain 1, 2, and 3
    when 88 is appended
    - should contain 1 and 88
- should have size 0 when created

Note: class PathAnyFreeSpec's approach to isolation was inspired in part by the specsy framework, written by Esko Luontola.

Shared fixtures

A test fixture is objects or other artifacts (such as files, sockets, database connections, etc.) used by tests to do their work. If a fixture is used by only one test, then the definitions of the fixture objects can be local to the method. If multiple tests need to share an immutable fixture, you can simply assign them to instance variables. If multiple tests need to share mutable fixture objects or vars, there's one and only one way to do it in a PathAnyFreeSpec: place the mutable objects lexically before the test. Any mutations needed by the test must be placed lexically before and/or after the test. As used here, "Lexically before" means that the code needs to be executed during construction of that test's instance of the test class to reach the test (or put another way, the code is along the "path to the test.") "Lexically after" means that the code needs to be executed to exit the constructor after the test has been executed.

The reason lexical placement is the one and only one way to share fixtures in a PathAnyFreeSpec is because all of its lifecycle methods are overridden and declared final. Thus you can't mix in BeforeAndAfter or BeforeAndAfterEach, because both override runTest, which is final in a PathAnyFreeSpec. You also can't override withFixture, because PathAnyFreeSpec extends Suite not TestSuite, where withFixture is defined. In short:

In a `path.FreeSpec`, if you need some code to execute before a test, place that code lexically before the test. If you need some code to execute after a test, place that code lexically after the test.

The reason the life cycle methods are final, by the way, is to prevent users from attempting to combine a PathAnyFreeSpec's approach to isolation with other ways ScalaTest provides to share fixtures or execute tests, because doing so could make the resulting test code hard to reason about. A PathAnyFreeSpec's execution model is a bit magical, but because it executes in one and only one way, users should be able to reason about the code. To help you visualize how a PathAnyFreeSpec is executed, consider the following variant of ExampleSpec that includes print statements:

import org.scalatest.freespec
import org.scalatest.matchers.Matchers
import scala.collection.mutable.ListBuffer

class ExampleSpec extends PathAnyFreeSpec with Matchers {

  println("Start of: ExampleSpec")
  "A ListBuffer" - {

    println("Start of: A ListBuffer")
    val buf = ListBuffer.empty[Int]

    "should be empty when created" in {

      println("In test: should be empty when created; buf is: " + buf)
      buf should be ('empty)
    }

    "when 1 is appended" - {

      println("Start of: when 1 is appended")
      buf += 1

      "should contain 1" in {

        println("In test: should contain 1; buf is: " + buf)
        buf.remove(0) should equal (1)
        buf should be ('empty)
      }

      "when 2 is appended" - {

        println("Start of: when 2 is appended")
        buf += 2

        "should contain 1 and 2" in {

          println("In test: should contain 1 and 2; buf is: " + buf)
          buf.remove(0) should equal (1)
          buf.remove(0) should equal (2)
          buf should be ('empty)
        }

        "when 2 is removed" - {

          println("Start of: when 2 is removed")
          buf -= 2

          "should contain only 1 again" in {

            println("In test: should contain only 1 again; buf is: " + buf)
            buf.remove(0) should equal (1)
            buf should be ('empty)
          }

          println("End of: when 2 is removed")
        }

        "when 3 is appended" - {

          println("Start of: when 3 is appended")
          buf += 3

          "should contain 1, 2, and 3" in {

            println("In test: should contain 1, 2, and 3; buf is: " + buf)
            buf.remove(0) should equal (1)
            buf.remove(0) should equal (2)
            buf.remove(0) should equal (3)
            buf should be ('empty)
          }
          println("End of: when 3 is appended")
        }

        println("End of: when 2 is appended")
      }

      "when 88 is appended" - {

        println("Start of: when 88 is appended")
        buf += 88

        "should contain 1 and 88" in {

          println("In test: should contain 1 and 88; buf is: " + buf)
          buf.remove(0) should equal (1)
          buf.remove(0) should equal (88)
          buf should be ('empty)
        }

        println("End of: when 88 is appended")
      }

      println("End of: when 1 is appended")
    }

    "should have size 0 when created" in {

      println("In test: should have size 0 when created; buf is: " + buf)
      buf should have size 0
    }

    println("End of: A ListBuffer")
  }
  println("End of: ExampleSpec")
  println()
}

Running the above version of ExampleSpec in the Scala interpreter will give you output similar to:

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

scala> run(new ExampleSpec)
ExampleSpec:
Start of: ExampleSpec
Start of: A ListBuffer
In test: should be empty when created; buf is: ListBuffer()
End of: A ListBuffer
End of: ExampleSpec

Start of: ExampleSpec
Start of: A ListBuffer
Start of: when 1 is appended
In test: should contain 1; buf is: ListBuffer(1)
ExampleSpec:
End of: when 1 is appended
End of: A ListBuffer
End of: ExampleSpec

Start of: ExampleSpec
Start of: A ListBuffer
Start of: when 1 is appended
Start of: when 2 is appended
In test: should contain 1 and 2; buf is: ListBuffer(1, 2)
End of: when 2 is appended
End of: when 1 is appended
End of: A ListBuffer
End of: ExampleSpec

Start of: ExampleSpec
Start of: A ListBuffer
Start of: when 1 is appended
Start of: when 2 is appended
Start of: when 2 is removed
In test: should contain only 1 again; buf is: ListBuffer(1)
End of: when 2 is removed
End of: when 2 is appended
End of: when 1 is appended
End of: A ListBuffer
End of: ExampleSpec

Start of: ExampleSpec
Start of: A ListBuffer
Start of: when 1 is appended
Start of: when 2 is appended
Start of: when 3 is appended
In test: should contain 1, 2, and 3; buf is: ListBuffer(1, 2, 3)
End of: when 3 is appended
End of: when 2 is appended
End of: when 1 is appended
End of: A ListBuffer
End of: ExampleSpec

Start of: ExampleSpec
Start of: A ListBuffer
Start of: when 1 is appended
Start of: when 88 is appended
In test: should contain 1 and 88; buf is: ListBuffer(1, 88)
End of: when 88 is appended
End of: when 1 is appended
End of: A ListBuffer
End of: ExampleSpec

Start of: ExampleSpec
Start of: A ListBuffer
In test: should have size 0 when created; buf is: ListBuffer()
End of: A ListBuffer
End of: ExampleSpec

A ListBuffer
- should be empty when created
  when 1 is appended
  - should contain 1
    when 2 is appended
    - should contain 1 and 2
      when 2 is removed
      - should contain only 1 again
      when 3 is appended
      - should contain 1, 2, and 3
    when 88 is appended
    - should contain 1 and 88
- should have size 0 when created

Note that each test is executed in order of appearance in the PathAnyFreeSpec, and that only those println statements residing in blocks that enclose the test being run are executed. Any println statements in blocks that do not form the "path" to a test are not executed in the instance of the class that executes that test.

How it executes

To provide its special brand of test isolation, PathAnyFreeSpec executes quite differently from its sister class in org.scalatest.freespec. An org.scalatest.freespec.PathAnyFreeSpec registers tests during construction and executes them when run is invoked. An org.scalatest.path.FreeSpec, by contrast, runs each test in its own instance while that instance is being constructed. During construction, it registers not the tests to run, but the results of running those tests. When run is invoked on a PathAnyFreeSpec, it reports the registered results and does not run the tests again. If run is invoked a second or third time, in fact, a PathAnyFreeSpec will each time report the same results registered during construction. If you want to run the tests of a PathAnyFreeSpec anew, you'll need to create a new instance and invoke run on that.

A PathAnyFreeSpec will create one instance for each "leaf" node it contains. The main kind of leaf node is a test, such as:

// One instance will be created for each test
"should be empty when created" in {
  buf should be ('empty)
}

However, an empty scope (a scope that contains no tests or nested scopes) is also a leaf node:

// One instance will be created for each empty scope
"when 99 is added" - {
  // A scope is "empty" and therefore a leaf node if it has no
  // tests or nested scopes, though it may have other code (which
  // will be executed in the instance created for that leaf node)
  buf += 99
}

The tests will be executed sequentially, in the order of appearance. The first test (or empty scope, if that is first) will be executed when a class that mixes in path.FreeSpec is instantiated. Only the first test will be executed during this initial instance, and of course, only the path to that test. Then, the first time the client uses the initial instance (by invoking one of run, expectedTestsCount, tags, or testNames on the instance), the initial instance will, before doing anything else, ensure that any remaining tests are executed, each in its own instance.

To ensure that the correct path is taken in each instance, and to register its test results, the initial PathAnyFreeSpec instance must communicate with the other instances it creates for running any subsequent leaf nodes. It does so by setting a thread-local variable prior to creating each instance (a technique suggested by Esko Luontola). Each instance of PathAnyFreeSpec checks the thread-local variable. If the thread-local is not set, it knows it is an initial instance and therefore executes every block it encounters until it discovers, and executes the first test (or empty scope, if that's the first leaf node). It then discovers, but does not execute the next leaf node, or discovers there are no other leaf nodes remaining to execute. It communicates the path to the next leaf node, if any, and the result of running the test it did execute, if any, back to the initial instance. The initial instance repeats this process until all leaf nodes have been executed and all test results registered.

Ignored tests

You mark a test as ignored in an org.scalatest.freespec.PathAnyFreeSpec in the same manner as in an org.scalatest.freespec.AnyFreeSpec. Please see the Ignored tests section in its documentation for more information.

Note that a separate instance will be created for an ignored test, and the path to the ignored test will be executed in that instance, but the test function itself will not be executed. Instead, a TestIgnored event will be fired.

Informers

You output information using Informers in an org.scalatest.freespec.PathAnyFreeSpec in the same manner as in an org.scalatest.freespec.AnyFreeSpec. Please see the Informers section in its documentation for more information.

Pending tests

You mark a test as pending in an org.scalatest.freespec.PathAnyFreeSpec in the same manner as in an org.scalatest.freespec.AnyFreeSpec. Please see the Pending tests section in its documentation for more information.

Note that a separate instance will be created for a pending test, and the path to the ignored test will be executed in that instance, as well as the test function (up until it completes abruptly with a TestPendingException).

Tagging tests

You can place tests into groups by tagging them in an org.scalatest.freespec.PathAnyFreeSpec in the same manner as in an org.scalatest.freespec.AnyFreeSpec. Please see the Tagging tests section in its documentation for more information.

Note that one difference between this class and its sister class org.scalatest.freespec.AnyFreeSpec is that because tests are executed at construction time, rather than each time run is invoked, an org.scalatest.freespec.PathAnyFreeSpec will always execute all non-ignored tests. When run is invoked on a PathAnyFreeSpec, if some tests are excluded based on tags, the registered results of running those tests will not be reported. (But those tests will have already run and the results registered.) By contrast, because an org.scalatest.freespec.PathAnyFreeSpec only executes tests after run has been called, and at that time the tags to include and exclude are known, only tests selected by the tags will be executed.

In short, in an org.scalatest.freespec.AnyFreeSpec, tests not selected by the tags to include and exclude specified for the run (via the Filter passed to run) will not be executed. In an org.scalatest.freespec.PathAnyFreeSpec, by contrast, all non-ignored tests will be executed, each during the construction of its own instance, and tests not selected by the tags to include and exclude specified for a run will not be reported. (One upshot of this is that if you have tests that you want to tag as being slow so you can sometimes exclude them during a run, you probably don't want to put them in a PathAnyFreeSpec. Because in a PathFreespec the slow tests will be run regardless, with only their registered results not being reported if you exclude slow tests during a run.)

Shared tests

You can factor out shared tests in an org.scalatest.freespec.PathAnyFreeSpec in the same manner as in an org.scalatest.freespec.AnyFreeSpec. Please see the Shared tests section in its documentation for more information.

Nested suites

Nested suites are not allowed in a PathAnyFreeSpec. Because a PathAnyFreeSpec executes tests eagerly at construction time, registering the results of those test runs and reporting them later when run is invoked, the order of nested suites versus test runs would be different in a org.scalatest.freespec.PathAnyFreeSpec than in an org.scalatest.freespec.AnyFreeSpec. In org.scalatest.freespec.AnyFreeSpec's implementation of run, nested suites are executed then tests are executed. A org.scalatest.freespec.PathAnyFreeSpec with nested suites would execute these in the opposite order: first tests then nested suites. To help make PathAnyFreeSpec code easier to reason about by giving readers of one less difference to think about, nested suites are not allowed. If you want to add nested suites to a PathAnyFreeSpec, you can instead wrap them all in a Suites object. They will be executed in the order of appearance (unless a Distributor is passed, in which case they will execute in parallel).

Durations

Many ScalaTest events include a duration that indicates how long the event being reported took to execute. For example, a TestSucceeded event provides a duration indicating how long it took for that test to execute. A SuiteCompleted event provides a duration indicating how long it took for that entire suite of tests to execute.

In the test completion events fired by a PathAnyFreeSpec (TestSucceeded, TestFailed, or TestPending), the durations reported refer to the time it took for the tests to run. This time is registered with the test results and reported along with the test results each time run is invoked. By contrast, the suite completion events fired for a path.FreeSpec represent the amount of time it took to report the registered results. (These events are not fired by path.FreeSpec, but instead by the entity that invokes run on the path.FreeSpec.) As a result, the total time for running the tests of a PathAnyFreeSpec, calculated by summing the durations of all the individual test completion events, may be greater than the duration reported for executing the entire suite.

trait PathAnyFreeSpecLike extends Suite with OneInstancePerTest with Informing with Notifying with Alerting with Documenting
Implementation trait for class PathAnyFreeSpec, which is a sister class to org.scalatest.freespec.AnyFreeSpec that isolates tests by running each test in its own instance of the test class, and for each test, only executing the path leading to that test.
Implementation trait for class PathAnyFreeSpec, which is a sister class to org.scalatest.freespec.AnyFreeSpec that isolates tests by running each test in its own instance of the test class, and for each test, only executing the path leading to that test.
PathAnyFreeSpec 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 PathAnyFreeSpec into some other class, you can use this trait instead, because class PathAnyFreeSpec does nothing more than extend this trait and add a nice toString implementation.
See the documentation of the class for a detailed overview of PathAnyFreeSpec.

Packages

freespec

package freespec

Type Members

Ignored tests

Informers

Documenters

Notifiers and alerters

Pending tests

Tagging tests

Shared fixtures

Calling get-fixture methods

Instantiating fixture-context objects

Overriding withFixture(NoArgTest)

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

Sharing fixtures across classes

Sharing fixtures across classes

Shared fixtures

How it executes

Ignored tests

Informers

Pending tests

Tagging tests

Shared tests

Nested suites

Durations

Inherited from AnyRef

Inherited from Any

Ungrouped

freespec

Overriding `withFixture(NoArgTest)`

Overriding `withFixture(OneArgTest)`

Mixing in `BeforeAndAfter`

Overriding `withFixture(NoArgAsyncTest)`

Overriding `withFixture(OneArgTest)`

Mixing in `BeforeAndAfter`