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. Bothfeature and scenario are methods, defined inFeatureSpec, 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 toscenario, which will register the test for later execution.

A FeatureSpec's lifecycle has two phases: the registration phase and theready phase. It starts in registration phase and enters ready phase the first timerun 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 aTestRegistrationClosedException.

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 theReporter. 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

Shared fixtures

A test fixture is objects or other artifacts (such as files, sockets, database connections, etc.) used by tests to do their work. You can use fixtures inFeatureSpecs with the same approaches suggested for Suite in its documentation. The same text that appears in the test fixture section of Suite's documentation is repeated here, with examples changed fromSuite to FeatureSpec.

If a fixture is used by only one test, then the definitions of the fixture objects can be local to the test function, such as the objects assigned to stack and emptyStack in the previous StackFeatureSpec examples. If multiple tests need to share a fixture, the best approach is to assign them to instance variables. Here's a (very contrived) example, in which the object assigned to shared is used by multiple test functions:

import org.scalatest.FeatureSpec
class ArithmeticFeatureSpec extends FeatureSpec {
  // Sharing immutable fixture objects via instance variables
  val shared = 5
  feature("Integer arithmetic") {
    scenario("addition") {
      val sum = 2 + 3
      assert(sum === shared)
    }
    scenario("subtraction") {
      val diff = 7 - 2
      assert(diff === shared)
    }
  }
}

In some cases, however, shared mutable fixture objects may be changed by tests 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 offers methods setUp andtearDown for this purpose. In ScalaTest, you can use the BeforeAndAfterEach trait, which will be described later, to implement an approach similar to JUnit's setUpand tearDown, however, this approach often involves reassigning vars between tests. Before going that route, you should consider some approaches that avoid vars. One approach is to write one or more create-fixture methods that return a new instance of a needed object (or a tuple or case class holding new instances of multiple objects) each time it is called. You can then call a create-fixture method at the beginning of each test that needs the fixture, storing the fixture object or objects in local variables. Here's an example:

import org.scalatest.FeatureSpec
import scala.collection.mutable.ListBuffer
class MyFeatureSpec extends FeatureSpec {
  // create objects needed by tests and return as a tuple
  def createFixture = (
    new StringBuilder("ScalaTest is "),
    new ListBuffer[String]
  )
  feature("The create-fixture approach") {
    scenario("shared fixture objects are mutated by a test") {
      val (builder, lbuf) = createFixture
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(lbuf.isEmpty)
      lbuf += "sweet"
    }
    scenario("test gets a fresh copy of the shared fixture") {
      val (builder, lbuf) = createFixture
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(lbuf.isEmpty)
    }
  }
}

If different tests in the same FeatureSpec require different fixtures, you can create multiple create-fixture methods and call the method (or methods) needed by each test at the begining of the test. If every test requires the same set of mutable fixture objects, one other approach you can take is make them simply vals and mix in traitOneInstancePerTest. If you mix in OneInstancePerTest, each test will be run in its own instance of the FeatureSpec, similar to the way JUnit tests are executed.

Although the create-fixture 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, one option is to mix in the BeforeAndAfterEach trait.BeforeAndAfterEach's beforeEach method will be run before, and its afterEachmethod after, each test (like JUnit's setUp and tearDownmethods, respectively). For example, you could create a temporary file before each test, and delete it afterwords, like this:

import org.scalatest.FeatureSpec
import org.scalatest.BeforeAndAfterEach
import java.io.FileReader
import java.io.FileWriter
import java.io.File
class FileIoFeatureSpec extends FeatureSpec with BeforeAndAfterEach {
  private val FileName = "TempFile.txt"
  private var reader: FileReader = _
  // Set up the temp file needed by the test
  override def beforeEach() {
    val writer = new FileWriter(FileName)
    try {
      writer.write("Hello, test!")
    }
    finally {
      writer.close()
    }
    // Create the reader needed by the test
    reader = new FileReader(FileName)
  }
  // Close and delete the temp file
  override def afterEach() {
    reader.close()
    val file = new File(FileName)
    file.delete()
  }
  feature("Reading and writing files") {
    scenario("reading from a temp file") {
      var builder = new StringBuilder
      var c = reader.read()
      while (c != -1) {
        builder.append(c.toChar)
        c = reader.read()
      }
      assert(builder.toString === "Hello, test!")
    }
    scenario("reading first char of a temp file") {
      assert(reader.read() === 'H')
    }
    scenario("no fixture is passed") {
      assert(1 + 1 === 2)
    }
  }
}

In this example, the instance variable reader is a var, so it can be reinitialized between tests by the beforeEach method.

Although the BeforeAndAfterEach approach should be familiar to the users of most test other frameworks, ScalaTest provides another alternative that also allows you to perform cleanup after each test: overriding withFixture(NoArgTest). To execute each test, Suite's implementation of the runTest method wraps an invocation of the appropriate test method in a no-arg function. runTest passes that test function to the withFixture(NoArgTest)method, which is responsible for actually running the test by invoking the function. Suite's implementation of withFixture(NoArgTest) simply invokes the function, like this:

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

The withFixture(NoArgTest) method exists so that you can override it and set a fixture up before, and clean it up after, each test. Thus, the previous temp file example could also be implemented without mixing in BeforeAndAfterEach, like this:

import org.scalatest.FeatureSpec
import org.scalatest.BeforeAndAfterEach
import java.io.FileReader
import java.io.FileWriter
import java.io.File
class FileIoFeatureSpec extends FeatureSpec {
  private var reader: FileReader = _
  override def withFixture(test: NoArgTest) {
    val FileName = "TempFile.txt"
    // Set up the temp file needed by the test
    val writer = new FileWriter(FileName)
    try {
      writer.write("Hello, test!")
    }
    finally {
      writer.close()
    }
    // Create the reader needed by the test
    reader = new FileReader(FileName)
    try {
      test() // Invoke the test function
    }
    finally {
      // Close and delete the temp file
      reader.close()
      val file = new File(FileName)
      file.delete()
    }
  }
  feature("Reading and writing files") {
    scenario("reading from a temp file") {
      var builder = new StringBuilder
      var c = reader.read()
      while (c != -1) {
        builder.append(c.toChar)
        c = reader.read()
      }
      assert(builder.toString === "Hello, test!")
    }
    scenario("reading first char of a temp file") {
      assert(reader.read() === 'H')
    }
    scenario("no fixture is passed") {
      assert(1 + 1 === 2)
    }
  }
}

If you prefer to keep your test classes immutable, one final variation is to use theFixtureFeatureSpec trait from theorg.scalatest.fixture package. Tests in an org.scalatest.fixture.FixtureFeatureSpec can have a fixture object passed in as a parameter. You must indicate the type of the fixture object by defining the Fixture type member and define a withFixture method that takes a one-arg test function. (A FixtureFeatureSpec has two overloaded withFixture methods, therefore, one that takes a OneArgTestand the other, inherited from Suite, that takes a NoArgTest.) Inside the withFixture(OneArgTest) method, you create the fixture, pass it into the test function, then perform any necessary cleanup after the test function returns. Instead of invoking each test directly, a FixtureFeatureSpec will pass a function that invokes the code of a test to withFixture(OneArgTest). Your withFixture(OneArgTest) method, therefore, is responsible for actually running the code of the test by invoking the test function. For example, you could pass the temp file reader fixture to each test that needs it by overriding the withFixture(OneArgTest) method of a FixtureFeatureSpec, like this:

import org.scalatest.fixture.FixtureFeatureSpec
import java.io.FileReader
import java.io.FileWriter
import java.io.File
class MySuite extends FixtureFeatureSpec {
  type FixtureParam = FileReader
  def withFixture(test: OneArgTest) {
    val FileName = "TempFile.txt"
    // Set up the temp file needed by the test
    val writer = new FileWriter(FileName)
    try {
      writer.write("Hello, test!")
    }
    finally {
      writer.close()
    }
    // Create the reader needed by the test
    val reader = new FileReader(FileName)
    try {
      // Run the test using the temp file
      test(reader)
    }
    finally {
      // Close and delete the temp file
      reader.close()
      val file = new File(FileName)
      file.delete()
    }
  }
  feature("Reading and writing files") {
    scenario("reading from a temp file") { reader =>
      var builder = new StringBuilder
      var c = reader.read()
      while (c != -1) {
        builder.append(c.toChar)
        c = reader.read()
      }
      assert(builder.toString === "Hello, test!")
    }
    scenario("reading first char of a temp file") { reader =>
      assert(reader.read() === 'H')
    }
    scenario("no fixture is passed") { () =>
      assert(1 + 1 === 2)
    }
  }
}

It is worth noting that the only difference in the test code between the mutableBeforeAndAfterEach approach shown here and the immutable FixtureFeatureSpecapproach shown previously is that two of the FixtureFeatureSpec's test functions take a FileReader as a parameter via the "reader =>" at the beginning of the function. Otherwise the test code is identical. One benefit of the explicit parameter is that, as demonstrated by the "no fixture passed" scenario, a FixtureFeatureSpectest need not take the fixture. So you can have some tests that take a fixture, and others that don't. In this case, the FixtureFeatureSpec provides documentation indicating which tests use the fixture and which don't, whereas the BeforeAndAfterEach approach does not. (If you have want to combine tests that take different fixture types in the same FeatureSpec, you can use MultipleFixtureFeatureSpec.)

If you want to execute code before and after all tests (and nested suites) in a suite, such as you could do with @BeforeClass and @AfterClassannotations in JUnit 4, you can use the beforeAll and afterAllmethods of BeforeAndAfterAll. See the documentation for BeforeAndAfterAll for an example.

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) inbehavior 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 var buf = new ListBuffer[T]
  def push(o: T) {
    if (!full)
      o +: buf
    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 Spec'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 aFeatureSpec, 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)

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.groups.SlowTest andcom.mycompany.groups.DbTest, then you could create matching groups for FeatureSpecs like this:

import org.scalatest.Tag
object SlowTest extends Tag("com.mycompany.groups.SlowTest")
object DbTest extends Tag("com.mycompany.groups.DbTest")

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

import org.scalatest.FeatureSpec
class ArithmeticFeatureSpec 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.groups.SlowTest tag, and test "subtraction" with the com.mycompany.groups.DbTest tag.

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

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 ArithmeticFeatureSpec 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 ArithmeticFeatureSpec with:

scala> (new ArithmeticFeatureSpec).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 primary 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 Reporteris 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 ArithmeticFeatureSpec 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 ArithmeticFeatureSpec 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 FeatureSpecto 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 ArithmeticFeatureSpec).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, the 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 ArithmeticFeatureSpec 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 ArithmeticFeatureSpec with:

scala> (new ArithmeticFeatureSpec).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