FeatureSpec

A suite of tests in which each test represents one scenario of a feature. FeatureSpec is intended for writing tests that are "higher level" than unit tests, for example, integration tests, functional tests, and acceptance tests. You can use FeatureSpec for unit testing if you prefer, however. Here's an example:

import org.scalatest.FeatureSpec
import org.scalatest.GivenWhenThen
import scala.collection.mutable.Stack

class StackFeatureSpec extends FeatureSpec with GivenWhenThen {

  feature("The user can pop an element off the top of the stack") {

    info("As a programmer")
    info("I want to be able to pop items off the stack")
    info("So that I can get them in last-in-first-out order")

    scenario("pop is invoked on a non-empty stack") {

      given("a non-empty stack")
      val stack = new Stack[Int]
      stack.push(1)
      stack.push(2)
      val oldSize = stack.size

      when("when pop is invoked on the stack")
      val result = stack.pop()

      then("the most recently pushed element should be returned")
      assert(result === 2)

      and("the stack should have one less item than before")
      assert(stack.size === oldSize - 1)
    }

    scenario("pop is invoked on an empty stack") {

      given("an empty stack")
      val emptyStack = new Stack[String]

      when("when pop is invoked on the stack")
      then("NoSuchElementException should be thrown")
      intercept[NoSuchElementException] {
        emptyStack.pop()
      }

      and("the stack should still be empty")
      assert(emptyStack.isEmpty)
    }
  }
}

A FeatureSpec contains feature clauses and scenarios. You define a feature clause with feature, and a scenario with scenario. Both feature and scenario are methods, defined in FeatureSpec, which will be invoked by the primary constructor of StackFeatureSpec. A feature clause describes a feature of the subject (class or other entity) you are specifying and testing. In the previous example, the subject under specification and test is a stack. The feature being specified and tested is the ability for a user (a programmer in this case) to pop an element off the top of the stack. With each scenario you provide a string (the spec text) that specifies the behavior of the subject for one scenario in which the feature may be used, and a block of code that tests that behavior. You place the spec text between the parentheses, followed by the test code between curly braces. The test code will be wrapped up as a function passed as a by-name parameter to scenario, which will register the test for later execution.

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

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

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

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

scala> (new StackFeatureSpec).execute()

You would see:

Feature: The user can pop an element off the top of the stack
  As a programmer
  I want to be able to pop items off the stack
  So that I can get them in last-in-first-out order
  Scenario: pop is invoked on a non-empty stack
    Given a non-empty stack
    When when pop is invoked on the stack
    Then the most recently pushed element should be returned
    And the stack should have one less item than before
  Scenario: pop is invoked on an empty stack
    Given an empty stack
    When when pop is invoked on the stack
    Then NoSuchElementException should be thrown
    And the stack should still be empty

See also: Getting started with FeatureSpec.

Ignored tests

To support the common use case of “temporarily” disabling a test, with the good intention of resurrecting the test at a later time, FeatureSpec provides registration methods that start with ignore instead of scenario. For example, to temporarily disable the test named addition, just change “scenario” into “ignore,” like this:

import org.scalatest.FeatureSpec

class ArithmeticSpec extends FeatureSpec {

  // Sharing fixture objects via instance variables
  val shared = 5

  feature("Integer arithmetic") {

    ignore("addition") {
      val sum = 2 + 3
      assert(sum === shared)
    }

    scenario("subtraction") {
      val diff = 7 - 2
      assert(diff === shared)
    }
  }
}

If you run this version of ArithmeticSpec with:

scala> (new ArithmeticSpec).execute()

It will run only subtraction and report that addition was ignored:

Feature: Integer arithmetic 
  Scenario: addition !!! IGNORED !!!
  Scenario: subtraction

Informers

One of the parameters to the 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 FeatureSpec's methods will be sufficient, but occasionally you may wish to provide custom information to the Reporter from a test. For this purpose, an Informer that will forward information to the current Reporter is provided via the info parameterless method. You can pass the extra information to the Informer via its apply method. The Informer will then pass the information to the Reporter via an InfoProvided event. Here's an example:

import org.scalatest.FeatureSpec

class ArithmeticSpec extends FeatureSpec {

  feature("Integer arithmetic") {

    scenario("addition") {
      val sum = 2 + 3
      assert(sum === 5)
      info("Addition seems to work")
    }

    scenario("subtraction") {
      val diff = 7 - 2
      assert(diff === 5)
    }
  }
}

If you run this ArithmeticSpec from the interpreter, you will see the following message included in the printed report:

Feature: Integer arithmetic
  Scenario: addition
    Addition seems to work

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

import org.scalatest.FeatureSpec
import org.scalatest.GivenWhenThen

class ArithmeticSpec extends FeatureSpec with GivenWhenThen {

  feature("Integer arithmetic") {

    scenario("addition") {

      given("two integers")
      val x = 2
      val y = 3

      when("they are added")
      val sum = x + y

      then("the result is the sum of the two numbers")
      assert(sum === 5)
    }

    scenario("subtraction") {

      given("two integers")
      val x = 7
      val y = 2

      when("one is subtracted from the other")
      val diff = x - y

      then("the result is the difference of the two numbers")
      assert(diff === 5)
    }
  }
}

If you run this FeatureSpec from the interpreter, you will see the following messages included in the printed report:

scala> (new ArithmeticSpec).execute()
Feature: Integer arithmetic
  Scenario: addition
    Given two integers
    When they are added
    Then the result is the sum of the two numbers
  Scenario: subtraction
    Given two integers
    When one is subtracted from the other
    Then the result is the difference of the two numbers

Pending tests

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

To support this style of testing, a test can be given a name that specifies one bit of behavior required by the system being tested. The test can also include some code that sends more information about the behavior to the reporter when the tests run. At the end of the test, it can call method pending, which will cause it to complete abruptly with TestPendingException.

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

import org.scalatest.FeatureSpec

class ArithmeticSpec extends FeatureSpec {

  // Sharing fixture objects via instance variables
  val shared = 5

  feature("Integer arithmetic") {

    scenario("addition") {
      val sum = 2 + 3
      assert(sum === shared)
    }

    scenario("subtraction") (pending)
  }
}

(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 ArithmeticSpec with:

scala> (new ArithmeticSpec).execute()

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

Feature: Integer arithmetic
  Scenario: addition
  Scenario: subtraction (pending)

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

One other difference between ignored and pending tests is that ignored tests are implemented as a test tag that is excluded by default. Thus an ignored test is never executed. By contrast, a pending test is implemented as a test that throws TestPendingException (which is what calling the pending method does). Thus the body of pending tests are executed up until they throw TestPendingException. The reason for this difference is that it enables your unfinished test to send InfoProvided messages to the reporter before it completes abruptly with TestPendingException, as shown in the previous example on Informers that used the GivenWhenThen trait. For example, the following snippet in a FeatureSpec:

feature("Integer arithmetic") {
    scenario("addition") {
      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:

Feature: Integer arithmetic
  Scenario: addition (pending)
    Given two integers
    When they are added
    Then the result is the sum of the two numbers

Tagging tests

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

import org.scalatest.Tag

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

Given these definitions, you could place FeatureSpec tests into groups like this:

import org.scalatest.FeatureSpec

class ArithmeticSpec extends FeatureSpec {

  // Sharing fixture objects via instance variables
  val shared = 5

  feature("Integer arithmetic") {

    scenario("addition", SlowTest) {
      val sum = 2 + 3
      assert(sum === shared)
    }

    scenario("subtraction", SlowTest, DbTest) {
      val diff = 7 - 2
      assert(diff === shared)
    }
  }
}

This code marks both tests, "addition" and "subtraction," with the com.mycompany.tags.SlowTest tag, and test "subtraction" with the com.mycompany.tags.DbTest tag.

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

Shared fixtures

A test fixture is 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 method, then the definitions of the fixture objects can be local to the method, such as the objects assigned to sum and diff in the previous ExampleSpec examples. If multiple methods need to share an immutable fixture, one approach is to assign them to instance variables.

In some cases, however, shared mutable fixture objects may be changed by test methods such that they need to be recreated or reinitialized before each test. Shared resources such as files or database connections may also need to be created and initialized before, and cleaned up after, each test. JUnit 3 offered methods setUp and tearDown for this purpose. In ScalaTest, you can use the BeforeAndAfterEach trait, which will be described later, to implement an approach similar to JUnit's setUp and tearDown, however, this approach usually involves reassigning vars or mutating objects between tests. Before going that route, you may wish to consider some more functional approaches that avoid side effects.

Calling create-fixture methods

One approach is to write one or more create-fixture methods that return a new instance of a needed fixture object (or an holder object containing multiple needed fixture objects) each time it is called. You can then call a create-fixture method at the beginning of each test method that needs the fixture, storing the returned object or objects in local variables. Here's an example:

import org.scalatest.FeatureSpec
import collection.mutable.ListBuffer

class ExampleSpec extends FeatureSpec {

  def fixture =
    new {
      val builder = new StringBuilder("ScalaTest is ")
      val buffer = new ListBuffer[String]
    }

  feature("Fixtures can be shared") {

    scenario("user learns how to share fixtures") {
      val f = fixture
      f.builder.append("easy!")
      assert(f.builder.toString === "ScalaTest is easy!")
      assert(f.buffer.isEmpty)
      f.buffer += "sweet"
    }

    scenario("user enjoys writing tests with shared fixtures") {
      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.

Instantiating fixture traits

A related technique is to place the fixture objects in a fixture trait and run your test code in the context of a new anonymous class instance that mixes in the fixture trait, like this:

import org.scalatest.FeatureSpec
import collection.mutable.ListBuffer

class ExampleSpec extends FeatureSpec {

  trait Fixture {
    val builder = new StringBuilder("ScalaTest is ")
    val buffer = new ListBuffer[String]
  }

  feature("Fixtures can be shared") {

    scenario("user learns how to share fixtures") {
      new Fixture {
        builder.append("easy!")
        assert(builder.toString === "ScalaTest is easy!")
        assert(buffer.isEmpty)
        buffer += "sweet"
      }
    }

    scenario("user enjoys writing tests with shared fixtures") {
      new Fixture {
        builder.append("fun!")
        assert(builder.toString === "ScalaTest is fun!")
        assert(buffer.isEmpty)
      }
    }
  }
}

Mixing in OneInstancePerTest

If every test method requires the same set of mutable fixture objects, one other approach you can take is make them simply vals and mix in trait OneInstancePerTest. If you mix in OneInstancePerTest, each test will be run in its own instance of the Suite, similar to the way JUnit tests are executed. Here's an example:

import org.scalatest.FeatureSpec
import org.scalatest.OneInstancePerTest
import collection.mutable.ListBuffer

class ExampleSpec extends FeatureSpec with OneInstancePerTest {

  val builder = new StringBuilder("ScalaTest is ")
  val buffer = new ListBuffer[String]

  feature("Fixtures can be shared") {

    scenario("user learns how to share fixtures") {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    scenario("user enjoys writing tests with shared fixtures") {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
    }
  }
}

Although the create-fixture, fixture-trait, and OneInstancePerTest approaches take care of setting up a fixture before each test, they don't address the problem of cleaning up a fixture after the test completes. In this situation, you'll need to either use side effects or the loan pattern.

Mixing in BeforeAndAfter

One way to use side effects is to mix in the BeforeAndAfter trait. 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:

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

class ExampleSpec extends FeatureSpec with BeforeAndAfter {

  val builder = new StringBuilder
  val buffer = new ListBuffer[String]

  before {
    builder.append("ScalaTest is ")
  }

  after {
    builder.clear()
    buffer.clear()
  }

  feature("Fixtures can be shared") {

    scenario("user learns how to share fixtures") {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    scenario("user enjoys writing tests with shared fixtures") {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
    }
  }
}

Overriding withFixture(NoArgTest)

An alternate way to take care of setup and cleanup via side effects is to override withFixture. Trait Suite's implementation of runTest, which is inherited by this trait, passes a no-arg test function to withFixture. It is withFixture's responsibility to invoke that test function. Suite's implementation of withFixture simply invokes the function, like this:

// Default implementation
protected def withFixture(test: NoArgTest) {
  test()
}

You can, therefore, override withFixture to perform setup before, and 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. Here's an example:

import org.scalatest.FeatureSpec
import collection.mutable.ListBuffer

class ExampleSpec extends FeatureSpec {

  val builder = new StringBuilder
  val buffer = new ListBuffer[String]

  override def withFixture(test: NoArgTest) {
    builder.append("ScalaTest is ") // perform setup
    try {
      test() // invoke the test function
    }
    finally {
      builder.clear() // perform cleanup
      buffer.clear()
    }
  }

  feature("Fixtures can be shared") {

    scenario("user learns how to share fixtures") {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    scenario("user enjoys writing tests with shared fixtures") {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }
  }
}

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

The reason you should perform cleanup in a finally clause is that withFixture is called by runTest, which expects an exception to be thrown to indicate a failed test. Thus when you invoke the test function inside withFixture, it may complete abruptly with an exception. The finally clause will ensure the fixture cleanup happens as that exception propagates back up the call stack to runTest.

Overriding withFixture(OneArgTest)

To use the loan pattern, you can extend FeatureSpec (from the org.scalatest.fixture package) instead of FeatureSpec. Each test in a FeatureSpec takes a fixture as a parameter, allowing you to pass the fixture into the test. You must indicate the type of the fixture parameter by specifying FixtureParam, and implement a withFixture method that takes a OneArgTest. This withFixture method is responsible for invoking the one-arg test function, so you can perform fixture set up before, and clean up after, invoking and passing the fixture into the test function. Here's an example:

import org.scalatest.fixture
import java.io.FileWriter
import java.io.File

class ExampleSpec extends fixture.FeatureSpec {

  final val tmpFile = "temp.txt"

  type FixtureParam = FileWriter

  def withFixture(test: OneArgTest) {

    val writer = new FileWriter(tmpFile) // set up the fixture
    try {
      test(writer) // "loan" the fixture to the test
    }
    finally {
      writer.close() // clean up the fixture
    }
  }

  feature("Fixtures can be shared") {

    scenario("user learns how to share fixtures") { writer =>
      writer.write("Hello, test!")
      writer.flush()
      assert(new File(tmpFile).length === 12)
    }

    scenario("user enjoys writing tests with shared fixtures") { writer =>
      writer.write("Hi, test!")
      writer.flush()
      assert(new File(tmpFile).length === 9)
    }
  }
}

For more information, see the documentation for FeatureSpec.

Providing different fixtures to different tests

If different tests in the same FeatureSpec require different fixtures, you can combine the previous techniques and provide each test with just the fixture or fixtures it needs. Here's an example in which a StringBuilder and a ListBuffer are provided via fixture traits, and file writer (that requires cleanup) is provided via the loan pattern:

import java.io.FileWriter
import java.io.File
import collection.mutable.ListBuffer
import org.scalatest.FeatureSpec

class ExampleSpec extends FeatureSpec {

  final val tmpFile = "temp.txt"

  trait Builder {
    val builder = new StringBuilder("ScalaTest is ")
  }

  trait Buffer {
    val buffer = ListBuffer("ScalaTest", "is")
  }

  def withWriter(testCode: FileWriter => Any) {
    val writer = new FileWriter(tmpFile) // set up the fixture
    try {
      testCode(writer) // "loan" the fixture to the test
    }
    finally {
      writer.close() // clean up the fixture
    }
  }

  scenario("user is productive using the test framework") { // This test needs the StringBuilder fixture
    new Builder {
      builder.append("productive!")
      assert(builder.toString === "ScalaTest is productive!")
    }
  }

  scenario("tests are readable") { // This test needs the ListBuffer[String] fixture
    new Buffer {
      buffer += ("readable!")
      assert(buffer === List("ScalaTest", "is", "readable!"))
    }
  }

  scenario("the test framework is user-friendly") { // This test needs the FileWriter fixture
    withWriter { writer =>
      writer.write("Hello, user!")
      writer.flush()
      assert(new File(tmpFile).length === 12)
    }
  }

  scenario("test code is clear and concise") { // This test needs the StringBuilder and ListBuffer
    new Builder with Buffer {
      builder.append("clear!")
      buffer += ("concise!")
      assert(builder.toString === "ScalaTest is clear!")
      assert(buffer === List("ScalaTest", "is", "concise!"))
    }
  }

  scenario("user composes test artifacts") { // This test needs all three fixtures
    new Builder with Buffer {
      builder.append("clear!")
      buffer += ("concise!")
      assert(builder.toString === "ScalaTest is clear!")
      assert(buffer === List("ScalaTest", "is", "concise!"))
      withWriter { writer =>
        writer.write(builder.toString)
        writer.flush()
        assert(new File(tmpFile).length === 19)
      }
    }
  }
}

In the previous example, "user is productive using the test framework uses only the StringBuilder fixture, so it just instantiates a new Builder, whereas tests are readable uses only the ListBuffer fixture, so it just intantiates a new Buffer. the test framework is user-friendly needs just the FileWriter fixture, so it invokes withWriter, which prepares and passes a FileWriter to the test (and takes care of closing it afterwords).

Two tests need multiple fixtures: test code is clear and concise needs both the StringBuilder and the ListBuffer, so it instantiates a class that mixes in both fixture traits with new Builder with Buffer. user composes test artifacts needs all three fixtures, so in addition to new Builder with Buffer it also invokes withWriter, wrapping just the of the test code that needs the fixture.

Note that in this case, the loan pattern is being implemented via the withWriter method that takes a function, not by overriding FeatureSpec's withFixture(OneArgTest) method. FeatureSpec makes the most sense if all (or at least most) tests need the same fixture, whereas in this Suite only two tests need the FileWriter.

In the previous example, the withWriter method passed an object into the tests. Passing fixture objects into tests is generally a good idea when possible, but sometimes a side affect is unavoidable. For example, if you need to initialize a database running on a server across a network, your with-fixture method will likely have nothing to pass. In such cases, simply create a with-fixture method that takes a by-name parameter and performs setup and cleanup via side effects, like this:

def withDataInDatabase(test: => Any) {
  // initialize the database across the network
  try {
    test // "loan" the initialized database to the test
  }
  finally {
    // clean up the database
  }
}

You can then use it like:

scenario("user logs in") {
  withDataInDatabase {
    // test user logging in scenario
  }
}

Composing stackable fixture 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:

import org.scalatest.FeatureSpec
import org.scalatest.AbstractSuite
import collection.mutable.ListBuffer

trait Builder extends AbstractSuite { this: Suite =>

  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 AbstractSuite { this: Suite =>

  val buffer = new ListBuffer[String]

  abstract override def withFixture(test: NoArgTest) {
    try {
      super.withFixture(test) // To be stackable, must call super.withFixture
    }
    finally {
      buffer.clear()
    }
  }
}

class ExampleSpec extends FeatureSpec with Builder with Buffer {

  feature("Fixtures can be shared") {

    scenario("user learns how to share fixtures") {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    scenario("user enjoys writing tests with shared fixtures") {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }
  }
}

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

class Example2Spec extends FeatureSpec with Buffer with Builder

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

class Example3Spec extends FeatureSpec with Builder

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

import org.scalatest.FeatureSpec
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 FeatureSpec with Builder with Buffer {

  feature("Fixtures can be shared") {

    scenario("user learns how to share fixtures") {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    scenario("user enjoys writing tests with shared fixtures") {
      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.afterAll throws an exception.

One difference to bear in mind between the before-and-after traits and the withFixture methods, is that if a withFixture method completes abruptly with an exception, it is considered a failed test. By contrast, if any of the methods on the before-and-after traits (i.e., before and after of BeforeAndAfter, beforeEach and afterEach of BeforeAndAfterEach, and beforeAll and afterAll of BeforeAndAfterAll) complete abruptly, it is considered a failed suite, which will result in a SuiteAborted event.

Shared scenarios

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

import scala.collection.mutable.ListBuffer

class Stack[T] {

  val MAX = 10
  private val buf = new ListBuffer[T]

  def push(o: T) {
    if (!full)
      buf.prepend(o)
    else
      throw new IllegalStateException("can't push onto a full stack")
  }

  def pop(): T = {
    if (!empty)
      buf.remove(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def peek: T = {
    if (!empty)
      buf(0)
    else
      throw new IllegalStateException("can't pop an empty stack")
  }

  def full: Boolean = buf.size == MAX
  def empty: Boolean = buf.size == 0
  def size = buf.size

  override def toString = buf.mkString("Stack(", ", ", ")")
}

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

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

import org.scalatest.FeatureSpec
import org.scalatest.GivenWhenThen
import org.scalatestexamples.helpers.Stack

trait FeatureSpecStackBehaviors { this: FeatureSpec with GivenWhenThen =>

  def nonEmptyStack(createNonEmptyStack: => Stack[Int], lastItemAdded: Int) {

    scenario("empty is invoked on this non-empty stack: " + createNonEmptyStack.toString) {

      given("a non-empty stack")
      val stack = createNonEmptyStack

      when("empty is invoked on the stack")
      then("empty returns false")
      assert(!stack.empty)
    }

    scenario("peek is invoked on this non-empty stack: " + createNonEmptyStack.toString) {

      given("a non-empty stack")
      val stack = createNonEmptyStack
      val size = stack.size

      when("peek is invoked on the stack")
      then("peek returns the last item added")
      assert(stack.peek === lastItemAdded)

      and("the size of the stack is the same as before")
      assert(stack.size === size)
    }

    scenario("pop is invoked on this non-empty stack: " + createNonEmptyStack.toString) {

      given("a non-empty stack")
      val stack = createNonEmptyStack
      val size = stack.size

      when("pop is invoked on the stack")
      then("pop returns the last item added")
      assert(stack.pop === lastItemAdded)

      and("the size of the stack one less than before")
      assert(stack.size === size - 1)
    }
  }

  def nonFullStack(createNonFullStack: => Stack[Int]) {

    scenario("full is invoked on this non-full stack: " + createNonFullStack.toString) {

      given("a non-full stack")
      val stack = createNonFullStack

      when("full is invoked on the stack")
      then("full returns false")
      assert(!stack.full)
    }

    scenario("push is invoked on this non-full stack: " + createNonFullStack.toString) {

      given("a non-full stack")
      val stack = createNonFullStack
      val size = stack.size

      when("push is invoked on the stack")
      stack.push(7)

      then("the size of the stack is one greater than before")
      assert(stack.size === size + 1)

      and("the top of the stack contains the pushed value")
      assert(stack.peek === 7)
    }
  }
}

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

scenariosFor(nonEmptyStack(stackWithOneItem, lastValuePushed))
scenariosFor(nonFullStack(stackWithOneItem))

If you prefer to use an imperative style to change fixtures, for example by mixing in BeforeAndAfterEach and reassigning a stack var in beforeEach, you could write your behavior functions in the context of that var, which means you wouldn't need to pass in the stack fixture because it would be in scope already inside the behavior function. In that case, your code would look like this:

scenariosFor(nonEmptyStack) // assuming lastValuePushed is also in scope inside nonEmptyStack
scenariosFor(nonFullStack)

The recommended style, however, is the functional, pass-all-the-needed-values-in style. Here's an example:

import org.scalatest.FeatureSpec
import org.scalatest.GivenWhenThen
import org.scalatestexamples.helpers.Stack

class StackFeatureSpec extends FeatureSpec with GivenWhenThen with FeatureSpecStackBehaviors {

  // Stack fixture creation methods
  def emptyStack = new Stack[Int]

  def fullStack = {
    val stack = new Stack[Int]
    for (i <- 0 until stack.MAX)
      stack.push(i)
    stack
  }

  def stackWithOneItem = {
    val stack = new Stack[Int]
    stack.push(9)
    stack
  }

  def stackWithOneItemLessThanCapacity = {
    val stack = new Stack[Int]
    for (i <- 1 to 9)
      stack.push(i)
    stack
  }

  val lastValuePushed = 9

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

    scenario("empty is invoked on an empty stack") {

      given("an empty stack")
      val stack = emptyStack

      when("empty is invoked on the stack")
      then("empty returns true")
      assert(stack.empty)
    }

    scenario("peek is invoked on an empty stack") {

      given("an empty stack")
      val stack = emptyStack

      when("peek is invoked on the stack")
      then("peek throws IllegalStateException")
      intercept[IllegalStateException] {
        stack.peek
      }
    }

    scenario("pop is invoked on an empty stack") {

      given("an empty stack")
      val stack = emptyStack

      when("pop is invoked on the stack")
      then("pop throws IllegalStateException")
      intercept[IllegalStateException] {
        emptyStack.pop
      }
    }

    scenariosFor(nonEmptyStack(stackWithOneItem, lastValuePushed))
    scenariosFor(nonFullStack(stackWithOneItem))

    scenariosFor(nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed))
    scenariosFor(nonFullStack(stackWithOneItemLessThanCapacity))

    scenario("full is invoked on a full stack") {

      given("an full stack")
      val stack = fullStack

      when("full is invoked on the stack")
      then("full returns true")
      assert(stack.full)
    }

    scenariosFor(nonEmptyStack(fullStack, lastValuePushed))

    scenario("push is invoked on a full stack") {

      given("an full stack")
      val stack = fullStack

      when("push is invoked on the stack")
      then("push throws IllegalStateException")
      intercept[IllegalStateException] {
        stack.push(10)
      }
    }
  }
}

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

scala> (new StackFeatureSpec).execute()
Feature: A Stack is pushed and popped
  Scenario: empty is invoked on an empty stack
    Given an empty stack
    When empty is invoked on the stack
    Then empty returns true
  Scenario: peek is invoked on an empty stack
    Given an empty stack
    When peek is invoked on the stack
    Then peek throws IllegalStateException
  Scenario: pop is invoked on an empty stack
    Given an empty stack
    When pop is invoked on the stack
    Then pop throws IllegalStateException
  Scenario: empty is invoked on this non-empty stack: Stack(9)
    Given a non-empty stack
    When empty is invoked on the stack
    Then empty returns false
  Scenario: peek is invoked on this non-empty stack: Stack(9)
    Given a non-empty stack
    When peek is invoked on the stack
    Then peek returns the last item added
    And the size of the stack is the same as before
  Scenario: pop is invoked on this non-empty stack: Stack(9)
    Given a non-empty stack
    When pop is invoked on the stack
    Then pop returns the last item added
    And the size of the stack one less than before
  Scenario: full is invoked on this non-full stack: Stack(9)
    Given a non-full stack
    When full is invoked on the stack
    Then full returns false
  Scenario: push is invoked on this non-full stack: Stack(9)
    Given a non-full stack
    When push is invoked on the stack
    Then the size of the stack is one greater than before
    And the top of the stack contains the pushed value
  Scenario: empty is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
    Given a non-empty stack
    When empty is invoked on the stack
    Then empty returns false
  Scenario: peek is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
    Given a non-empty stack
    When peek is invoked on the stack
    Then peek returns the last item added
    And the size of the stack is the same as before
  Scenario: pop is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
    Given a non-empty stack
    When pop is invoked on the stack
    Then pop returns the last item added
    And the size of the stack one less than before
  Scenario: full is invoked on this non-full stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
    Given a non-full stack
    When full is invoked on the stack
    Then full returns false
  Scenario: push is invoked on this non-full stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
    Given a non-full stack
    When push is invoked on the stack
    Then the size of the stack is one greater than before
    And the top of the stack contains the pushed value
  Scenario: full is invoked on a full stack
    Given an full stack
    When full is invoked on the stack
    Then full returns true
  Scenario: empty is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
    Given a non-empty stack
    When empty is invoked on the stack
    Then empty returns false
  Scenario: peek is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
    Given a non-empty stack
    When peek is invoked on the stack
    Then peek returns the last item added
    And the size of the stack is the same as before
  Scenario: pop is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
    Given a non-empty stack
    When pop is invoked on the stack
    Then pop returns the last item added
    And the size of the stack one less than before
  Scenario: push is invoked on a full stack
    Given an full stack
    When push is invoked on the stack
    Then push throws IllegalStateException

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. In a FeatureSpec there is no nesting construct analogous to FunSpec's describe clause. Therefore, you need to do a bit of extra work to ensure that the test names are unique. If a duplicate test name problem shows up in a FeatureSpec, you'll need to pass in a prefix or suffix string to add to each test name. You can pass this string the same way you pass any other data needed by the shared tests, or just call toString on the shared fixture object. This is the approach taken by the previous FeatureSpecStackBehaviors example.

Given this FeatureSpecStackBehaviors trait, calling it with the stackWithOneItem fixture, like this:

scenariosFor(nonEmptyStack(stackWithOneItem, lastValuePushed))

yields test names:

• empty is invoked on this non-empty stack: Stack(9)
• peek is invoked on this non-empty stack: Stack(9)
• pop is invoked on this non-empty stack: Stack(9)

Whereas calling it with the stackWithOneItemLessThanCapacity fixture, like this:

scenariosFor(nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed))

yields different test names:

• empty is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
• peek is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)
• pop is invoked on this non-empty stack: Stack(9, 8, 7, 6, 5, 4, 3, 2, 1)