Spec

Trait that facilitates a “behavior-driven” style of development (BDD), in which tests are combined with text that specifies the behavior the tests verify. (Note: In BDD, the word example is usually used instead of test. The word test will not appear in your code if you use WordSpec, so if you prefer the word example you can use it. However, in this documentation the word test will be used, for clarity and to be consistent with the rest of ScalaTest.) Here's an example Spec:

import org.scalatest.Spec
import scala.collection.mutable.Stack
class StackSpec extends Spec {
  describe("A Stack") {
    it("should pop values in last-in-first-out order") {
      val stack = new Stack[Int]
      stack.push(1)
      stack.push(2)
      assert(stack.pop() === 2)
      assert(stack.pop() === 1)
    }
    it("should throw NoSuchElementException if an empty stack is popped") {
      val emptyStack = new Stack[String]
      intercept[NoSuchElementException] {
        emptyStack.pop()
      }
    }
  }
}

A Spec contains describe clauses and tests. You define a describe clause with describe, and a test with it. Bothdescribe and it are methods, defined inSpec, which will be invoked by the primary constructor of StackSpec. A describe clause names, or gives more information about, the subject (class or other entity) you are specifying and testing. In the previous example, "A Stack" is the subject under specification and test. With each test you provide a string (the spec text) that specifies one bit of behavior of the subject, and a block of code that tests that behavior. You place the spec text between the parentheses, followed by the test code between curly braces. The test code will be wrapped up as a function passed as a by-name parameter toit, which will register the test for later execution.

A Spec'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.

Tests can only be registered with the it method while the Spec is in its registration phase. Any attempt to register a test after the Spec has entered its ready phase, i.e., after run has been invoked on the Spec, will be met with a thrown TestRegistrationClosedException. The recommended style of using Spec 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.

When you execute a Spec, 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 StackSpec from within the Scala interpreter:

scala> (new StackSpec).execute()

You would see:

A Stack
- should pop values in last-in-first-out order
- should throw NoSuchElementException if an empty stack is popped

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 inSpecs 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 Spec.

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 StackSpec 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.Spec
class ArithmeticSpec extends Spec {
  // Sharing immutable fixture objects via instance variables
  val shared = 5
  it("should add correctly") {
    val sum = 2 + 3
    assert(sum === shared)
  }
  it("should subtract correctly") {
    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.Spec
import scala.collection.mutable.ListBuffer
class MySpec extends Spec {
  // create objects needed by tests and return as a tuple
  def createFixture = (
    new StringBuilder("ScalaTest is "),
    new ListBuffer[String]
  )
  it("should mutate shared fixture objects") {
    val (builder, lbuf) = createFixture
    builder.append("easy!")
    assert(builder.toString === "ScalaTest is easy!")
    assert(lbuf.isEmpty)
    lbuf += "sweet"
  }
  it("should get a fresh set of mutable fixture objects") {
    val (builder, lbuf) = createFixture
    builder.append("fun!")
    assert(builder.toString === "ScalaTest is fun!")
    assert(lbuf.isEmpty)
  }
}

If different tests in the same Spec 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 Spec, 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.Spec
import org.scalatest.BeforeAndAfterEach
import java.io.FileReader
import java.io.FileWriter
import java.io.File
class MySpec extends Spec 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()
  }
  it("should read 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!")
  }
  it("should read the first char of a temp file") {
    assert(reader.read() === 'H')
  }
  it("should work without a fixture") {
    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.Spec
import org.scalatest.BeforeAndAfterEach
import java.io.FileReader
import java.io.FileWriter
import java.io.File
class MySpec extends Spec {
  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()
    }
  }
  it("should read 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!")
  }
  it("should read the first char of a temp file") {
    assert(reader.read() === 'H')
  }
  it("should work without a fixture") {
    assert(1 + 1 === 2)
  }
}

If you prefer to keep your test classes immutable, one final variation is to use theFixtureSpec trait from theorg.scalatest.fixture package. Tests in an org.scalatest.fixture.FixtureSpec 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 FixtureSpec 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 FixtureSpec 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 FixtureSpec, like this:

import org.scalatest.fixture.FixtureSpec
import java.io.FileReader
import java.io.FileWriter
import java.io.File
class MySuite extends FixtureSpec {
  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()
    }
  }
  it("should read 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!")
  }
  it("should read the first char of a temp file") { reader =>
    assert(reader.read() === 'H')
  }
  it("should work without a fixture") { () =>
    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 FixtureSpecapproach shown previously is that two of the FixtureSpec'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 "should work without a fixture" test, a FixtureSpectest need not take the fixture. So you can have some tests that take a fixture, and others that don't. In this case, the FixtureSpec 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 Spec, you can use MultipleFixtureSpec.)

If you want to execute code before and after all tests (and nested suites) in a suite, such 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 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 Spec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any Spec that uses them, so that the tests they contain will be registered as tests in that Spec. 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 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 Spec 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 Spec that uses them. If they are shared between different Specs, however, you could also define them in a separate trait that is mixed into each Spec 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: Spec =>
  def nonEmptyStack(stack: Stack[Int], lastItemAdded: Int) {
    it("should be non-empty") {
      assert(!stack.empty)
    }
    it("should return the top item on peek") {
      assert(stack.peek === lastItemAdded)
    }
    it("should not remove the top item on peek") {
      val size = stack.size
      assert(stack.peek === lastItemAdded)
      assert(stack.size === size)
    }
    it("should remove the top item on pop") {
      val size = stack.size
      assert(stack.pop === lastItemAdded)
      assert(stack.size === size - 1)
    }
  }
  def nonFullStack(stack: Stack[Int]) {
    it("should not be full") {
      assert(!stack.full)
    }
    it("should add to the top on push") {
      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 Spec offers a DSL for the purpose, which looks like this:

it should behave like nonEmptyStack(stackWithOneItem, lastValuePushed)
it should behave like nonFullStack(stackWithOneItem)

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

it should behave like nonEmptyStack // assuming lastValuePushed is also in scope inside nonEmptyStack
it should behave like nonFullStack

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

class SharedTestExampleSpec extends Spec with StackBehaviors {
  // Stack fixture creation methods
  def emptyStack = new Stack[Int]
  def fullStack = {
    val stack = new Stack[Int]
    for (i <- 0 until stack.MAX)
      stack.push(i)
    stack
  }
  def stackWithOneItem = {
    val stack = new Stack[Int]
    stack.push(9)
    stack
  }
  def stackWithOneItemLessThanCapacity = {
    val stack = new Stack[Int]
    for (i <- 1 to 9)
      stack.push(i)
    stack
  }
  val lastValuePushed = 9
  describe("A Stack") {
    describe("(when empty)") {
      it("should be empty") {
        assert(emptyStack.empty)
      }
      it("should complain on peek") {
        intercept[IllegalStateException] {
          emptyStack.peek
        }
      }
      it("should complain on pop") {
        intercept[IllegalStateException] {
          emptyStack.pop
        }
      }
    }
    describe("(with one item)") {
      it should behave like nonEmptyStack(stackWithOneItem, lastValuePushed)
      it should behave like nonFullStack(stackWithOneItem)
    }
    describe("(with one item less than capacity)") {
      it should behave like nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed)
      it should behave like nonFullStack(stackWithOneItemLessThanCapacity)
    }
    describe("(full)") {
      it("should be full") {
        assert(fullStack.full)
      }
      it should behave like nonEmptyStack(fullStack, lastValuePushed)
      it("should complain on a push") {
        intercept[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> (new StackSpec).execute()
A Stack (when empty)
- should be empty
- should complain on peek
- should complain on pop
A Stack (with one item)
- should be non-empty
- should return the top item on peek
- should not remove the top item on peek
- should remove the top item on pop
- should not be full
- should add to the top on push
A Stack (with one item less than capacity)
- should be non-empty
- should return the top item on peek
- should not remove the top item on peek
- should remove the top item on pop
- should not be full
- should add to the top on push
A Stack (full)
- should be full
- should be non-empty
- should return the top item on peek
- should not remove the top item on peek
- should remove the top item on pop
- should complain on a push

One thing to keep in mind when using shared tests is that in ScalaTest, each test in a suite must have a unique name. If you register the same tests repeatedly in the same suite, one problem you may encounter is an exception at runtime complaining that multiple tests are being registered with the same test name. A good way to solve this problem in a Spec is to surround each invocation of a behavior function with a describe clause, which will prepend a string to each test name. For example, the following code in a Spec would register a test with the name "A Stack (when empty) should be empty":

  describe("A Stack") {
    describe("(when empty)") {
      it("should be empty") {
        assert(emptyStack.empty)
      }
      // ...

If the "should be empty" test was factored out into a behavior function, it could be called repeatedly so long as each invocation of the behavior function is inside a different set of describe clauses.

Tagging tests

A Spec's tests may be classified into groups by tagging them with string names. As with any suite, when executing a Spec, groups of tests can optionally be included and/or excluded. To tag a Spec's tests, you pass objects that extend abstract class org.scalatest.Tag to the methods that register tests, it 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 Specs 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 and com.mycompany.groups.DbTest, then you could create matching groups for Specs 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 Spec tests into groups like this:

import org.scalatest.Spec
class MySuite extends Spec {
  it("should add correctly", SlowTest) {
    val sum = 1 + 1
    assert(sum === 2)
    assert(sum + 2 === 4)
  }
  it("should subtract correctly", SlowTest, DbTest) {
    val diff = 4 - 1
    assert(diff === 3)
    assert(diff - 2 === 1)
  }
}

This code marks both tests with the com.mycompany.groups.SlowTest tag, and test "should subtract correctly" 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, Spec provides registration methods that start with ignore instead of it. For example, to temporarily disable the test with the name "should pop values in last-in-first-out order", just change “it” into “ignore,” like this:

import org.scalatest.Spec
import scala.collection.mutable.Stack
class StackSpec extends Spec {
  describe("A Stack") {
    ignore("should pop values in last-in-first-out order") {
      val stack = new Stack[Int]
      stack.push(1)
      stack.push(2)
      assert(stack.pop() === 2)
      assert(stack.pop() === 1)
    }
    it("should throw NoSuchElementException if an empty stack is popped") {
      val emptyStack = new Stack[String]
      intercept[NoSuchElementException] {
        emptyStack.pop()
      }
    }
  }
}

If you run this version of StackSpec with:

scala> (new StackSpec).execute()

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

A Stack
- should pop values in last-in-first-out order !!! IGNORED !!!
- should throw NoSuchElementException if an empty stack is popped

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 a test as pending in Spec by placing "(pending)" after the test name, like this:

import org.scalatest.Spec
import scala.collection.mutable.Stack
class StackSpec extends Spec {
  describe("A Stack") {
    it("should pop values in last-in-first-out order") {
      val stack = new Stack[Int]
      stack.push(1)
      stack.push(2)
      assert(stack.pop() === 2)
      assert(stack.pop() === 1)
    }
    it("should throw NoSuchElementException if an empty stack is popped") (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 StackSpec with:

scala> (new StackSpec).execute()

It will run both tests, but report that the test named "A stack should pop values in last-in-first-out order" is pending. You'll see:

A Stack
- should pop values in last-in-first-out order
- should throw NoSuchElementException if an empty stack is popped (pending)