Facilitates a “behavior-driven” style of development (BDD), in which tests are methods, optionally nested inside singleton objects defining textual scopes.

Here's an example RefSpec:

package org.scalatest.examples.spec

import org.scalatest.RefSpec

class SetSpec extends RefSpec {

  object `A Set` {
    object `when empty` {
      def `should have size 0` {
        assert(Set.empty.size === 0)
      }

      def `should produce NoSuchElementException when head is invoked` {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

A RefSpec can contain scopes and tests. You define a scope with a nested singleton object, and a test with a method. The names of both scope objects and test methods must be expressed in back ticks and contain at least one space character.

A space placed in backticks is encoded by the Scala compiler as $u0020, as illustrated here:

scala> def `an example` = ()
an$u0020example: Unit

RefSpec uses reflection to discover scope objects and test methods. During discovery, RefSpec will consider any nested singleton object whose name includes $u0020 a scope object, and any method whose name includes $u0020 a test method. It will ignore any singleton objects or methods that do not include a $u0020 character. Thus, RefSpec would not consider the following singleton object a scope object:

object `Set` { // Not discovered, because no space character
}

You can make such a scope discoverable by placing a space at the end, like this:

object `Set ` { // Discovered, because of the trailing space character
}

Rather than performing this discovery during construction, when instance variables used by scope objects may as yet be uninitialized, RefSpec performs discovery lazily, the first time a method needing the results of discovery is invoked. For example, methods run, runTests, tags, expectedTestCount, runTest, and testNames all ensure that scopes and tests have already been discovered prior to doing anything else. Discovery is performed, and the results recorded, only once for each RefSpec instance.

A scope names, or gives more information about, the subject (class or other entity) you are specifying and testing. In the previous example, `A Set` is the subject under specification and test. With each test name you provide a string (the test text) that specifies one bit of behavior of the subject, and a block of code (the body of the test method) that verifies that behavior.

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

scala> org.scalatest.run(new SetSpec)

You would see:

A Set
  when empty
  - should have size 0
  - should produce NoSuchElementException when head is invoked

Or, to run just the test named A Set when empty should have size 0, you could pass that test's name, or any unique substring of the name, such as "size 0" or even just "0". Here's an example:

scala> org.scalatest.run(new SetSuite, "size 0")
A Set
  when empty
  - should have size 0

You can also pass to execute a config map of key-value pairs, which will be passed down into suites and tests, as well as other parameters that configure the run itself. For more information on running in the Scala interpreter, see the documentation for the ScalaTest shell.

The execute method invokes a run method that takes two parameters. This run method, which actually executes the suite, will usually be invoked by a test runner, such as run, tools.Runner, a build tool, or an IDE.

The test methods shown in this example are parameterless. This is recommended even for test methods with obvious side effects. In production code you would normally declare no-arg, side-effecting methods as empty-paren methods, and call them with empty parentheses, to make it more obvious to readers of the code that they have a side effect. Whether or not a test method has a side effect, however, is a less important distinction than it is for methods in production code. Moreover, test methods are not normally invoked directly by client code, but rather through reflection by running the Suite that contains them, so a lack of parentheses on an invocation of a side-effecting test method would not normally appear in any client code. Given the empty parentheses do not add much value in the test methods case, the recommended style is to simply always leave them off.

Note: The approach of using backticks around test method names to make it easier to write descriptive test names was inspired by the SimpleSpec test framework, originally created by Coda Hale.

Ignored tests

To support the common use case of temporarily disabling a test in a RefSpec, with the good intention of resurrecting the test at a later time, you can annotate the test method with @Ignore. For example, to temporarily disable the test method with the name `should have size zero", just annotate it with @Ignore, like this:

package org.scalatest.examples.spec.ignore

import org.scalatest._

class SetSpec extends RefSpec {

  object `A Set` {
    object `when empty` {
      @Ignore def `should have size 0` {
        assert(Set.empty.size === 0)
      }

      def `should produce NoSuchElementException when head is invoked` {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

If you run this version of SetSpec with:

scala> org.scalatest.run(new SetSpec)

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

A Set
  when empty
  - should have size 0 !!! IGNORED !!!
  - should produce NoSuchElementException when head is invoked

If you wish to temporarily ignore an entire suite of tests, you can annotate the test class with @Ignore, like this:

package org.scalatest.examples.spec.ignoreall

import org.scalatest._

@Ignore
class SetSpec extends RefSpec {

  object `A Set` {
    object `when empty` {
      def `should have size 0` {
        assert(Set.empty.size === 0)
      }

      def `should produce NoSuchElementException when head is invoked` {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

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

scala> org.scalatest.run(new SetSpec)
SetSpec:
A Set
  when empty
  - should have size 0 !!! IGNORED !!!
  - should produce NoSuchElementException when head is invoked !!! IGNORED !!!

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

Informers

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

package org.scalatest.examples.spec.info

import collection.mutable
import org.scalatest._

class SetSpec extends RefSpec with GivenWhenThen {

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

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

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

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

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

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

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

Documenters

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

Here's an example RefSpec that uses markup:

package org.scalatest.examples.spec.markup

import collection.mutable
import org.scalatest._

class SetSpec extends RefSpec with GivenWhenThen {

  markup { """

Mutable Set
———--

A set is a collection that contains no duplicate elements.

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

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

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

    def empty: This

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

  """ }

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

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

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

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

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

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

Notifiers and alerters

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

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

package org.scalatest.examples.spec.note

import collection.mutable
import org.scalatest._

class SetSpec extends RefSpec {

  object `A mutable Set` {
    def `should allow an element to be added` {

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

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

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

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

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

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

Pending tests

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

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

Because tests in ScalaTest can be designated as pending with TestPendingException, both the test name and any information sent to the reporter when running the test can appear in the report of a test run. (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 RefSpec by using "{ pending }" as the body of the test method, like this:

package org.scalatest.examples.spec.pending

import org.scalatest._

class SetSpec extends RefSpec {

  object `A Set` {
    object `when empty` {
      def `should have size 0` { pending }

      def `should produce NoSuchElementException when head is invoked` {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

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

scala> org.scalatest.run(new SetSpec)

It will run both tests, but report that test "should have size 0" is pending. You'll see:

A Set
  when empty
  - should have size 0 (pending)
  - should produce NoSuchElementException when head is invoked

Tagging tests

A RefSpec's tests may be classified into groups by tagging them with string names. When executing a RefSpec, groups of tests can optionally be included and/or excluded. In this trait's implementation, tags are indicated by annotations attached to the test method. To create a new tag type to use in RefSpecs, simply define a new Java annotation that itself is annotated with the org.scalatest.TagAnnotation annotation. (Currently, for annotations to be visible in Scala programs via Java reflection, the annotations themselves must be written in Java.) For example, to create tags named SlowTest and DbTest, you would write in Java:

package org.scalatest.examples.spec.tagging;
import java.lang.annotation.*;
import org.scalatest.TagAnnotation;

@TagAnnotation
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.TYPE})
public @interface SlowTest {}

@TagAnnotation
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.TYPE})
public @interface DbTest {}

Given these annotations, you could tag RefSpec tests like this:

package org.scalatest.examples.spec.tagging

import org.scalatest.RefSpec

class SetSpec extends RefSpec {

  object `A Set` {
    object `when empty` {

      @SlowTest
      def `should have size 0` {
        assert(Set.empty.size === 0)
      }

      @SlowTest @DbTest
      def `should produce NoSuchElementException when head is invoked` {
        assertThrows[NoSuchElementException] {
          Set.empty.head
        }
      }
    }
  }
}

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 with tags listed in the tagsToExclude Set. If tagsToInclude is defined, only tests with tags mentioned in the tagsToInclude set, and not mentioned in tagsToExclude, will be run.

A tag annotation also allows you to tag all the tests of a RefSpec in one stroke by annotating the class. For more information and examples, see the documentation for class Tag.

Shared fixtures

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

ScalaTest recommends three techniques to eliminate such code duplication:

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

Each technique is geared towards helping you reduce code duplication without introducing instance vars, shared mutable objects, or other dependencies between tests. Eliminating shared mutable state across tests will make your test code easier to reason about and more amenable for parallel test execution.

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

Calling get-fixture methods

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

package org.scalatest.examples.spec.getfixture

import org.scalatest.RefSpec
import collection.mutable.ListBuffer

class ExampleSpec extends RefSpec {

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

  def fixture = new Fixture

  object `Testing ` {
    def `should be easy` {
      val f = fixture
      f.builder.append("easy!")
      assert(f.builder.toString === "ScalaTest is easy!")
      assert(f.buffer.isEmpty)
      f.buffer += "sweet"
    }

    def `should be fun` {
      val f = fixture
      f.builder.append("fun!")
      assert(f.builder.toString === "ScalaTest is fun!")
      assert(f.buffer.isEmpty)
    }
  }
}

The “f.” in front of each use of a fixture object provides a visual indication of which objects are part of the fixture, but if you prefer, you can import the the members with “import f._” and use the names directly.

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

Instantiating fixture-context objects

An alternate technique that is especially useful when different tests need different combinations of fixture objects is to define the fixture objects as instance variables of fixture-context objects whose instantiation forms the body of tests. Like get-fixture methods, fixture-context objects are only appropriate if you don't need to clean up the fixtures after using them.

To use this technique, you define instance variables intialized with fixture objects in traits and/or classes, then in each test instantiate an object that contains just the fixture objects needed by the test. Traits allow you to mix together just the fixture objects needed by each test, whereas classes allow you to pass data in via a constructor to configure the fixture objects. Here's an example in which fixture objects are partitioned into two traits and each test just mixes together the traits it needs:

package org.scalatest.examples.spec.fixturecontext

import collection.mutable.ListBuffer
import org.scalatest.RefSpec

class ExampleSpec extends RefSpec {

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

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

  object `Testing ` {
    // This test needs the StringBuilder fixture
    def `should be productive` {
      new Builder {
        builder.append("productive!")
        assert(builder.toString === "ScalaTest is productive!")
      }
    }
  }

  object `Test code` {
    // This test needs the ListBuffer[String] fixture
    def `should be readable` {
      new Buffer {
        buffer += ("readable!")
        assert(buffer === List("ScalaTest", "is", "readable!"))
      }
    }

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

Overriding withFixture(NoArgTest)

Although the get-fixture method and fixture-context object approaches take care of setting up a fixture at the beginning of each test, they don't address the problem of cleaning up a fixture at the end of the test. If you just need to perform a side-effect at the beginning or end of a test, and don't need to actually pass any fixture objects into the test, you can override withFixture(NoArgTest), one of ScalaTest's lifecycle methods defined in trait Suite.

Trait Suite's implementation of runTest passes a no-arg test function to withFixture(NoArgTest). It is withFixture's responsibility to invoke that test function. Suite's implementation of withFixture simply invokes the function, like this:

// Default implementation in trait Suite
protected def withFixture(test: NoArgTest) = {
  test()
}

You can, therefore, override withFixture to perform setup before and/or cleanup after invoking the test function. If you have cleanup to perform, you should invoke the test function inside a try block and perform the cleanup in a finally clause, in case an exception propagates back through withFixture. (If a test fails because of an exception, the test function invoked by withFixture will result in a Failed wrapping the exception. Nevertheless, best practice is to perform cleanup in a finally clause just in case an exception occurs.)

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

// Your implementation
override def withFixture(test: NoArgTest) = {
  // Perform setup
  try super.withFixture(test) // Invoke the test function
  finally {
    // Perform cleanup
  }
}

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

package org.scalatest.examples.spec.noargtest

import java.io.File
import org.scalatest._

class ExampleSpec extends RefSpec {

  override def withFixture(test: NoArgTest) = {

    super.withFixture(test) match {
      case failed: Failed =>
        val currDir = new File(".")
        val fileNames = currDir.list()
        info("Dir snapshot: " + fileNames.mkString(", "))
        failed
      case other => other
    }
  }

  object `This test` {
    def `should succeed` {
      assert(1 + 1 === 2)
    }

    def `should fail` {
      assert(1 + 1 === 3)
    }
  }
}

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

scala> org.scalatest.run(new ExampleSuite)
ExampleSuite:
This test
- should fail *** FAILED ***
  2 did not equal 3 (:33)
  + Dir snapshot: hello.txt, world.txt 
- should succeed

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

Calling loan-fixture methods

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

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

package org.scalatest.examples.spec.loanfixture

import java.util.concurrent.ConcurrentHashMap

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

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

class ExampleSpec extends RefSpec {

  def withDatabase(testCode: Db => Any) {
    val dbName = randomUUID.toString
    val db = createDb(dbName) // create the fixture
    try {
      db.append("ScalaTest is ") // perform setup
      testCode(db) // "loan" the fixture to the test
    }
    finally removeDb(dbName) // clean up the fixture
  }

  def withFile(testCode: (File, FileWriter) => Any) {
    val file = File.createTempFile("hello", "world") // create the fixture
    val writer = new FileWriter(file)
    try {
      writer.write("ScalaTest is ") // set up the fixture
      testCode(file, writer) // "loan" the fixture to the test
    }
    finally writer.close() // clean up the fixture
  }

  object `Testing ` {
    // This test needs the file fixture
    def `should be productive` {
      withFile { (file, writer) =>
        writer.write("productive!")
        writer.flush()
        assert(file.length === 24)
      }
    }
  }

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

    // This test needs both the file and the database
    def `should be clear and concise` {
      withDatabase { db =>
       withFile { (file, writer) => // loan-fixture methods compose
          db.append("clear!")
          writer.write("concise!")
          writer.flush()
          assert(db.toString === "ScalaTest is clear!")
          assert(file.length === 21)
        }
      }
    }
  }
}

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

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

Overriding withFixture(OneArgTest)

fixture.Spec is deprecated, please use fixture.FunSpec instead.

Mixing in BeforeAndAfter

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

package org.scalatest.examples.spec.beforeandafter

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

class ExampleSpec extends RefSpec with BeforeAndAfter {

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

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

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

  object `Testing ` {
    def `should be easy` {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    def `should be fun` {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
    }
  }
}

Note that the only way before and after code can communicate with test code is via some side-effecting mechanism, commonly by reassigning instance vars or by changing the state of mutable objects held from instance vals (as in this example). If using instance vars or mutable objects held from instance vals you wouldn't be able to run tests in parallel in the same instance of the test class unless you synchronized access to the shared, mutable state. This is why ScalaTest's ParallelTestExecution trait extends OneInstancePerTest. By running each test in its own instance of the class, each test has its own copy of the instance variables, so you don't need to synchronize. If you mixed ParallelTestExecution into the ExampleSuite above, the tests would run in parallel just fine without any synchronization needed on the mutable StringBuilder and ListBuffer[String] objects.

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

Composing fixtures by stacking traits

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

package org.scalatest.examples.spec.composingwithfixture

import org.scalatest._
import collection.mutable.ListBuffer

trait Builder extends TestSuiteMixin { this: TestSuite =>

  val builder = new StringBuilder

  abstract override def withFixture(test: NoArgTest) = {
    builder.append("ScalaTest is ")
    try super.withFixture(test) // To be stackable, must call super.withFixture
    finally builder.clear()
  }
}

trait Buffer extends TestSuiteMixin { this: TestSuite =>

  val buffer = new ListBuffer[String]

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

class ExampleSpec extends RefSpec with Builder with Buffer {

  object `Testing ` {
    def `should be easy` {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    def `should be fun` {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }
  }
}

By mixing in both the Builder and Buffer traits, 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 RefSpec with Buffer with Builder

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

class Example3Spec extends RefSpec with Builder

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

package org.scalatest.examples.spec.composingbeforeandaftereach

import org.scalatest._
import org.scalatest.BeforeAndAfterEach
import collection.mutable.ListBuffer

trait Builder extends BeforeAndAfterEach { this: Suite =>

  val builder = new StringBuilder

  override def beforeEach() {
    builder.append("ScalaTest is ")
    super.beforeEach() // To be stackable, must call super.beforeEach
  }

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally builder.clear()
  }
}

trait Buffer extends BeforeAndAfterEach { this: Suite =>

  val buffer = new ListBuffer[String]

  override def afterEach() {
    try super.afterEach() // To be stackable, must call super.afterEach
    finally buffer.clear()
  }
}

class ExampleSpec extends RefSpec with Builder with Buffer {

  object `Testing ` {
    def `should be easy` {
      builder.append("easy!")
      assert(builder.toString === "ScalaTest is easy!")
      assert(buffer.isEmpty)
      buffer += "sweet"
    }

    def `should be fun` {
      builder.append("fun!")
      assert(builder.toString === "ScalaTest is fun!")
      assert(buffer.isEmpty)
      buffer += "clear"
    }
  }
}

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

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

Shared tests

Because RefSpec represents tests as methods, you cannot share or otherwise dynamically generate tests. Instead, use static code generation if you want to generate tests in a RefSpec. In other words, write a program that statically generates the entire source file of a RefSpec subclass.