Suite

A suite of tests. A Suite instance encapsulates a conceptual suite (i.e., a collection) of tests.

This trait provides an interface that allows suites of tests to be run. Its implementation enables a default way of writing and executing tests. Subtraits and subclasses can override Suite's methods to enable other ways of writing and executing tests. This trait's default approach allows tests to be defined as methods whose name starts with "test." This approach is easy to understand, and a good way for Scala beginners to start writing tests. More advanced Scala programmers may prefer to mix together other Suite subtraits defined in ScalaTest, or create their own, to write tests in the way they feel makes them most productive. Here's a quick overview of some of the options to help you get started:

For JUnit 3 users

If you are using JUnit 3 (version 3.8 or earlier releases) and you want to write JUnit 3 tests in Scala, look atAssertionsForJUnit,ShouldMatchersForJUnit, andJUnit3Suite.

For JUnit 4 users

If you are using JUnit 4 and you want to write JUnit 4 tests in Scala, look atJUnitSuite, andJUnitRunner. With JUnitRunner, you can use any of the traits described here and still run your tests with JUnit 4.

For TestNG users

If you are using TestNG and you want to write TestNG tests in Scala, look atTestNGSuite.

For high-level testing

If you want to write tests at a higher level than unit tests, such as integration tests, acceptance tests, or functional tests, check out FeatureSpec.

For unit testing

If you prefer a behavior-driven development (BDD) style, in which tests are combined with text that specifies the behavior being tested, look atSpec,FlatSpec, andWordSpec. Otherwise, if you just want to write tests and don't want to combine testing with specifying, look atFunSuite or read on to learn how to write tests using this base trait, Suite.

To use this trait's approach to writing tests, simply create classes that extend Suite and define test methods. Test methods have names of the form testX, where X is some unique, hopefully meaningful, string. A test method must be public and can have any result type, but the most common result type is Unit. Here's an example:

import org.scalatest.Suite
class MySuite extends Suite {
  def testAddition() {
    val sum = 1 + 1
    assert(sum === 2)
    assert(sum + 2 === 4)
  }
  def testSubtraction() {
    val diff = 4 - 1
    assert(diff === 3)
    assert(diff - 2 === 1)
  }
}

You can run a Suite by invoking on it one of four overloaded executemethods. These methods, which print test results to the standard output, are intended to serve as a convenient way to run tests from within the Scala interpreter. For example, to run MySuite from within the Scala interpreter, you could write:

scala> (new MySuite).execute()

And you would see:

Test Starting - MySuite: testAddition
Test Succeeded - MySuite: testAddition
Test Starting - MySuite: testSubtraction
Test Succeeded - MySuite: testSubtraction

Or, to run just the testAddition method, you could write:

scala> (new MySuite).execute("testAddition")

And you would see:

Test Starting - MySuite: testAddition
Test Succeeded - MySuite: testAddition

Two other execute methods that are intended to be run from the interpreter accept a "config" map of key-value pairs (see Config map, below). Each of these execute methods invokes a run method takes seven parameters. This run method, which actually executes the suite, will usually be invoked by a test runner, such as org.scalatest.tools.Runner or an IDE. See the documentation for Runner for more detail.

Assertions and ===

Inside test methods in a Suite, you can write assertions by invoking assert and passing in a Boolean expression, such as:

val left = 2
val right = 1
assert(left == right)

If the passed expression is true, assert will return normally. If false,assert will complete abruptly with a TestFailedException. This exception is usually not caught by the test method, which means the test method itself will complete abruptly by throwing the TestFailedException. Any test method that completes abruptly with a TestFailedException or any Exception is considered a failed test. A test method that returns normally is considered a successful test.

If you pass a Boolean expression to assert, a failed assertion will be reported, but without reporting the left and right values. You can alternatively encode these values in a String passed as a second argument to assert, as in:

val left = 2
val right = 1
assert(left == right, left + " did not equal " + right)

Using this form of assert, the failure report will include the left and right values, thereby helping you debug the problem. However, ScalaTest provides the === operator to make this easier. (The === operator is defined in trait Assertions which trait Suite extends.) You use it like this:

val left = 2
val right = 1
assert(left === right)

Because you use === here instead of ==, the failure report will include the left and right values. For example, the detail message in the thrown TestFailedException from the assertshown previously will include, "2 did not equal 1". From this message you will know that the operand on the left had the value 2, and the operand on the right had the value 1.

If you're familiar with JUnit, you would use ===in a ScalaTest Suite where you'd use assertEquals in a JUnit TestCase. The === operator is made possible by an implicit conversion from Anyto Equalizer. If you're curious to understand the mechanics, see the documentation forEqualizer and the convertToEqualizer method.

Expected results

Although === provides a natural, readable extension to Scala's assert mechanism, as the operands become lengthy, the code becomes less readable. In addition, the === comparison doesn't distinguish between actual and expected values. The operands are just called left and right, because if one were named expected and the other actual, it would be difficult for people to remember which was which. To help with these limitations of assertions, Suite includes a method called expect that can be used as an alternative to assert with ===. To use expect, you place the expected value in parentheses after expect, followed by curly braces containing code that should result in the expected value. For example:

val a = 5
val b = 2
expect(2) {
  a - b
}

In this case, the expected value is 2, and the code being tested is a - b. This expectation will fail, and the detail message in the TestFailedException will read, "Expected 2, but got 3."

Intercepted exceptions

Sometimes you need to test whether a method throws an expected exception under certain circumstances, such as when invalid arguments are passed to the method. You can do this in the JUnit style, like this:

val s = "hi"
try {
  s.charAt(-1)
  fail()
}
catch {
  case _: IndexOutOfBoundsException => // Expected, so continue
}

If charAt throws IndexOutOfBoundsException as expected, control will transfer to the catch case, which does nothing. If, however, charAt fails to throw an exception, the next statement, fail(), will be executed. The fail method always completes abruptly with a TestFailedException, thereby signaling a failed test.

To make this common use case easier to express and read, ScalaTest provides an interceptmethod. You use it like this:

val s = "hi"
intercept[IndexOutOfBoundsException] {
  s.charAt(-1)
}

This code behaves much like the previous example. If charAt throws an instance of IndexOutOfBoundsException,intercept will return that exception. But if charAt completes normally, or throws a different exception, intercept will complete abruptly with a TestFailedException. The intercept method returns the caught exception so that you can inspect it further if you wish, for example, to ensure that data contained inside the exception has the expected values. Here's an example:

val s = "hi"
val caught =
  intercept[IndexOutOfBoundsException] {
    s.charAt(-1)
  }
assert(caught.getMessage === "String index out of range: -1")

Using other assertions

ScalaTest also supports another style of assertions via its matchers DSL. By mixing in trait ShouldMatchers, you can write suites that look like:

import org.scalatest.Suite
import org.scalatest.matchers.ShouldMatchers
class MySuite extends Suite with ShouldMatchers {
  def testAddition() {
    val sum = 1 + 1
    sum should equal (2)
    sum + 2 should equal (4)
  }
  def testSubtraction() {
    val diff = 4 - 1
    diff should equal (3)
    diff - 2 should equal (1)
  }
}

If you prefer the word "must" to the word "should," you can alternatively mix in trait MustMatchers.

If you are comfortable with assertion mechanisms from other test frameworks, chances are you can use them with ScalaTest. Any assertion mechanism that indicates a failure with an exception can be used as is with ScalaTest. For example, to use the assertEqualsmethods provided by JUnit or TestNG, simply import them and use them. (You will of course need to include the relevant JAR file for the framework whose assertions you want to use on either the classpath or runpath when you run your tests.) Here's an example in which JUnit's assertions are imported, then used within a ScalaTest suite:

import org.scalatest.Suite
import org.junit.Assert._
class MySuite extends Suite {
  def testAddition() {
    val sum = 1 + 1
    assertEquals(2, sum)
    assertEquals(4, sum + 2)
  }
  def testSubtraction() {
    val diff = 4 - 1
    assertEquals(3, diff)
    assertEquals(1, diff - 2)
  }
}

Nested suites

A Suite can refer to a collection of other Suites, which are called nested Suites. Those nested Suites can in turn have their own nested Suites, and so on. Large test suites can be organized, therefore, as a tree of nested Suites. This trait's run method, in addition to invoking its test methods, invokes run on each of its nested Suites.

A List of a Suite's nested Suites can be obtained by invoking itsnestedSuites method. If you wish to create a Suite that serves as a container for nested Suites, whether or not it has test methods of its own, simply override nestedSuitesto return a List of the nested Suites. Because this is a common use case, ScalaTest provides a convenience SuperSuite class, which takes a List of nested Suites as a constructor parameter. Here's an example:

import org.scalatest.Suite
class ASuite extends Suite
class BSuite extends Suite
class CSuite extends Suite
class AlphabetSuite extends SuperSuite(
  List(
    new ASuite,
    new BSuite,
    new CSuite
  )
)

If you now run AlphabetSuite, for example from the interpreter:

scala> (new AlphabetSuite).run()

You will see reports printed to the standard output that indicate nested suites—ASuite, BSuite, andCSuite—were run.

Note that Runner can discover Suites automatically, so you need not necessarily specify SuperSuites explicitly. See the documentation for Runner for more information.

Shared fixtures

A test fixture is objects or other artifacts (such as files, sockets, database connections, etc.) used by tests to do their work. If a fixture is used by only one test method, then the definitions of the fixture objects can be local to the method, such as the objects assigned to sum and diff in the previous MySuite examples. If multiple methods need to share an immutable fixture, one 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 methods:

import org.scalatest.Suite
class MySuite extends Suite {
  // Sharing immutable fixture objects via instance variables
  val shared = 5
  def testAddition() {
    val sum = 2 + 3
    assert(sum === shared)
  }
  def testSubtraction() {
    val diff = 7 - 2
    assert(diff === shared)
  }
}

In some cases, however, shared mutable fixture objects may be changed by test methods such that they need to be recreated or reinitialized before each test. Shared resources such as files or database connections may also need to be created and initialized before, and cleaned up after, each test. JUnit 3 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 usually involves reassigning vars between tests. Before going that route, you may wish to 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 method that needs the fixture, storing the fixture object or objects in local variables. Here's an example:

import org.scalatest.Suite
import scala.collection.mutable.ListBuffer
class MySuite extends Suite {
  // create objects needed by tests and return as a tuple
  def createFixture = (
    new StringBuilder("ScalaTest is "),
    new ListBuffer[String]
  )
  def testEasy() {
    val (builder, lbuf) = createFixture
    builder.append("easy!")
    assert(builder.toString === "ScalaTest is easy!")
    assert(lbuf.isEmpty)
    lbuf += "sweet"
  }
  def testFun() {
    val (builder, lbuf) = createFixture
    builder.append("fun!")
    assert(builder.toString === "ScalaTest is fun!")
    assert(lbuf.isEmpty)
  }
}

If different tests in the same Suite 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 method 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 Suite, 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.Suite
import org.scalatest.BeforeAndAfterEach
import java.io.FileReader
import java.io.FileWriter
import java.io.File
class MySuite extends Suite 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()
  }
  def testReadingFromTheTempFile() {
    var builder = new StringBuilder
    var c = reader.read()
    while (c != -1) {
      builder.append(c.toChar)
      c = reader.read()
    }
    assert(builder.toString === "Hello, test!")
  }
  def testFirstCharOfTheTempFile() {
    assert(reader.read() === 'H')
  }
  def testWithoutAFixture() {
    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.Suite
import java.io.FileReader
import java.io.FileWriter
import java.io.File
class MySuite extends Suite {
  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()
    }
  }
  def testReadingFromTheTempFile() {
    var builder = new StringBuilder
    var c = reader.read()
    while (c != -1) {
      builder.append(c.toChar)
      c = reader.read()
    }
    assert(builder.toString === "Hello, test!")
  }
  def testFirstCharOfTheTempFile() {
    assert(reader.read() === 'H')
  }
  def testWithoutAFixture() {
    assert(1 + 1 === 2)
  }
}

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

import org.scalatest.fixture.FixtureSuite
import java.io.FileReader
import java.io.FileWriter
import java.io.File
class MySuite extends FixtureSuite {
  // No vars needed in this one
  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, passing in the temp file reader
      test(reader)
    }
    finally {
      // Close and delete the temp file
      reader.close()
      val file = new File(FileName)
      file.delete()
    }
  }
  def testReadingFromTheTempFile(reader: FileReader) {
    var builder = new StringBuilder
    var c = reader.read()
    while (c != -1) {
      builder.append(c.toChar)
      c = reader.read()
    }
    assert(builder.toString === "Hello, test!")
  }
  def testFirstCharOfTheTempFile(reader: FileReader) {
    assert(reader.read() === 'H')
  }
  def testWithoutAFixture() {
    assert(1 + 1 === 2)
  }
}

It is worth noting that the only difference in the test code between the mutableBeforeAndAfterEach approach shown previously and the immutable FixtureSuiteapproach shown here is that two of the FixtureSuite's test methods take a FileReader as a parameter. Otherwise the test code is identical. One benefit of the explicit parameter is that, as demonstrated by the testWithoutAFixture method, a FixtureSuitetest method need not take the fixture. (Tests that don't take a fixture as a parameter are passed to the withFixturethat takes a NoArgTest, shown previously.) So you can have some tests that take a fixture, and others that don't. In this case, the FixtureSuite provides documentation indicating which test methods use the fixture and which don't, whereas the BeforeAndAfterEach approach does not.

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.

The config map

In some cases you may need to pass information to a suite of tests. For example, perhaps a suite of tests needs to grab information from a file, and you want to be able to specify a different filename during different runs. You can accomplish this in ScalaTest by passing the filename in the config map of key-value pairs, which is passed to run as a Map[String, Any]. The values in the config map are called "config objects," because they can be used to configuresuites, reporters, and tests.

You can specify a string config object is via the ScalaTest Runner, either via the command line or ScalaTest's ant task. (See the documentation for Runner for information on how to specify config objects on the command line.) The config map is passed to run, runNestedSuites, runTests, and runTest, so one way to access it in your suite is to override one of those methods. If you need to use the config map inside your tests, you can use one of the traits in the org.scalatest.fixture package. (See thedocumentation for FixtureSuitefor instructions on how to access the config map in tests.)

Tagging tests

A Suite's tests may be classified into groups by tagging them with string names. When executing a Suite, 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 Suites, 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 a tag named SlowAsMolasses, to use to mark slow tests, you would write in Java:

import java.lang.annotation.*;
import org.scalatest.TagAnnotation
@TagAnnotation
@Retention(RetentionPolicy.RUNTIME)