FlatSpec's no-nesting approach contrasts with traits Spec and WordSpec, which use nesting to reduce duplication of specification text. Although nesting does have the advantage of reducing text duplication, figuring out the full specification text for one test can require back-tracking out of several levels of nesting, mentally prepending each fragment of text encountered. Thus the tradeoff with the nesting approach of Spec and WordSpec is that they have less duplicated text at the cost of being a bit challenging to read. Trait FlatSpec offers the opposite tradeoff. In a FlatSpec text is duplicated more, but figuring out the full specification text for a particular test is easier. Here's an example FlatSpec:

 import org.scalatest.FlatSpec
 import scala.collection.mutable.Stack

 class StackSpec extends FlatSpec {

   behavior of "A Stack"

   it should "pop values in last-in-first-out order" in {
     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" in {
     val emptyStack = new Stack[String]
     intercept[NoSuchElementException] {
       emptyStack.pop()
     }
   }
 }
 

Note: you can you must or can as well as should in a FlatSpec. For example, instead of it should "pop..., you could write it must "pop... or it can "pop....

Instead of using a behavior of clause, you can alternatively use a shorthand syntax in which you replace the first it with the subject string, like this:

 import org.scalatest.FlatSpec
 import scala.collection.mutable.Stack

 class StackSpec extends FlatSpec {

   "A Stack" should "pop values in last-in-first-out order" in {
     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" in {
     val emptyStack = new Stack[String]
     intercept[NoSuchElementException] {
       emptyStack.pop()
     }
   }
 }
 

Running either of the two previous three versions of StackSpec in the Scala interpreter would yield:

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

In a FlatSpec you write a one (or more) sentence specification for each bit of behavior you wish to specify and test. Each specification sentence has a "subject," which is sometimes called the system under test (or SUT). The subject is the entity being specified and tested and also serves as the subject of the sentences you write for each test. Often you will want to write multiple tests for the same subject. In a FlatSpec, you name the subject once, with a behavior of clause or its shorthand, then write tests for that subject with it should/mustcan "do something" phrases. Each it refers to the most recently declared subject. For example, the four tests shown in this snippet are all testing a stack that contains one item:

 behavior of "A Stack (with one item)"

 it should "be non-empty" in {}

 it should "return the top item on peek" in {}

 it should "not remove the top item on peek" in {}

 it should "remove the top item on pop" in {}
 

The same is true if the tests are written using the shorthand notation:

 "A Stack (with one item)" should "be non-empty" in {}

 it should "return the top item on peek" in {}

 it should "not remove the top item on peek" in {}

 it should "remove the top item on pop" in {}
 

In a FlatSpec, therefore, to figure out what "it" means, you just scan vertically until you find the most recent use of behavior of or the shorthand notation.

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

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

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 in FlatSpecs 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 from Suite to FlatSpec.

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 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 functions:

 import org.scalatest.FlatSpec

 class ArithmeticSpec extends FlatSpec {

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

  "The Scala language" must "add correctly" in {
     val sum = 2 + 3
     assert(sum === shared)
   }

   it must "subtract correctly" in {
     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 and tearDown for this purpose. In ScalaTest, you can use the BeforeAndAfterEach trait, which will be described later, to implement an approach similar to JUnit's setUp and tearDown, however, this approach 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.FlatSpec
 import scala.collection.mutable.ListBuffer

 class MySuite extends FlatSpec {

   // create objects needed by tests and return as a tuple
   def createFixture = (
     new StringBuilder("ScalaTest is "),
     new ListBuffer[String]
   )

  "ScalaTest" can "be easy " in {
     val (builder, lbuf) = createFixture
     builder.append("easy!")
     assert(builder.toString === "ScalaTest is easy!")
     assert(lbuf.isEmpty)
     lbuf += "sweet"
   }

   it can "be fun" in {
     val (builder, lbuf) = createFixture
     builder.append("fun!")
     assert(builder.toString === "ScalaTest is fun!")
     assert(lbuf.isEmpty)
   }
 }
 

If different tests in the same FlatSpec 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 trait OneInstancePerTest. If you mix in OneInstancePerTest, each test will be run in its own instance of the FlatSpec, 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 afterEach method after, each test (like JUnit's setUp and tearDown methods, respectively). For example, you could create a temporary file before each test, and delete it afterwords, like this:

 import org.scalatest.FlatSpec
 import org.scalatest.BeforeAndAfterEach
 import java.io.FileReader
 import java.io.FileWriter
 import java.io.File

 class MySuite extends FlatSpec 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()
   }

  "A FileReader" should "read in the contents of a file correctly" in {
     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 in the first character of a file correctly" in {
     assert(reader.read() === 'H')
   }
 
   it should "work without a fixture" in {
     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.FlatSpec
 import org.scalatest.BeforeAndAfterEach
 import java.io.FileReader
 import java.io.FileWriter
 import java.io.File

 class MySuite extends FlatSpec {

   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()
     }
   }

  "A FileReader" should "read in the contents of a file correctly" in {
     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 in the first character of a file correctly" in {
     assert(reader.read() === 'H')
   }
 
   it should "work without a fixture" in {
     assert(1 + 1 === 2)
   }
 }
 

If you prefer to keep your test classes immutable, one final variation is to use the FixtureFlatSpec trait from the org.scalatest.fixture package. Tests in an org.scalatest.fixture.FixtureFlatSpec 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 FixtureFlatSpec has two overloaded withFixture methods, therefore, one that takes a OneArgTest and 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 FixtureFlatSpec 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 FixtureFlatSpec, like this:

 import org.scalatest.fixture.FixtureFlatSpec
 import java.io.FileReader
 import java.io.FileWriter
 import java.io.File
 
 class MySuite extends FixtureFlatSpec {

   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()
     }
   }
 
  "A FileReader" should "read in the contents of a file correctly" in { 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 in the first character of a file correctly" in { reader =>
     assert(reader.read() === 'H')
   }
 
   it should "work without a fixture" in { () =>
     assert(1 + 1 === 2)
   }
 }
 

It is worth noting that the only difference in the test code between the mutable BeforeAndAfterEach approach shown here and the immutable FixtureFlatSpec approach shown previously is that two of the FixtureFlatSpec'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 "it should work without a fixture" test, a FixtureFlatSpec test need not take the fixture. So you can have some tests that take a fixture, and others that don't. In this case, the FixtureFlatSpec 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 FlatSpec, you can use MultipleFixtureFlatSpec.)

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 @AfterClass annotations in JUnit 4, you can use the beforeAll and afterAll methods 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 FlatSpec, you first place shared tests in behavior functions. These behavior functions will be invoked during the construction phase of any FlatSpec that uses them, so that the tests they contain will be registered as tests in that FlatSpec. 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 FlatSpec 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 FlatSpec that uses them. If they are shared between different FlatSpecs, however, you could also define them in a separate trait that is mixed into each FlatSpec 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: FlatSpec =>
 
   def nonEmptyStack(stack: Stack[Int], lastItemAdded: Int) {
 
     it should "be non-empty" in {
       assert(!stack.empty)
     }  
 
     it should "return the top item on peek" in {
       assert(stack.peek === lastItemAdded)
     }
   
     it should "not remove the top item on peek" in {
       val size = stack.size
       assert(stack.peek === lastItemAdded)
       assert(stack.size === size)
     }
   
     it should "remove the top item on pop" in {
       val size = stack.size
       assert(stack.pop === lastItemAdded)
       assert(stack.size === size - 1)
     }
   }
   
   def nonFullStack(stack: Stack[Int]) {
       
     it should "not be full" in {
       assert(!stack.full)
     }
       
     it should "add to the top on push" in {
       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 FlatSpec 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 FlatSpec 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
 
   "A Stack (when empty)" should "be empty" in {
     assert(emptyStack.empty)
   }
 
   it should "complain on peek" in {
     intercept[IllegalStateException] {
       emptyStack.peek
     }
   }

   it should "complain on pop" in {
     intercept[IllegalStateException] {
       emptyStack.pop
     }
   }
 
   "A Stack (with one item)" should behave like nonEmptyStack(stackWithOneItem, lastValuePushed)

   it should behave like nonFullStack(stackWithOneItem)
     
   "A Stack (with one item less than capacity)" should behave like nonEmptyStack(stackWithOneItemLessThanCapacity, lastValuePushed)

   it should behave like nonFullStack(stackWithOneItemLessThanCapacity)
 
   "A Stack (full)" should "be full" in {
     assert(fullStack.full)
   }
 
   it should behave like nonEmptyStack(fullStack, lastValuePushed)
 
   it should "complain on a push" in {
     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 SharedTestExampleSpec).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 WordSpec is to make sure each invocation of a behavior function is in the context of a different set of when, verb (should, must, or can), and that clauses, which will prepend a string to each test name. For example, the following code in a WordSpec would register a test with the name "A Stack (when empty) should be empty":

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

Or, using the shorthand notation:

   "A Stack" when {
     "empty" should {
       "be empty" in {
         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 in the context of a different combination of when, verb, and that clauses.

Tagging tests

 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 FlatSpec tests into groups like this:

 import org.scalatest.FlatSpec

 class MySuite extends FlatSpec {

   "The Scala language" must "add correctly" taggedAs(SlowTest) in {
       val sum = 1 + 1
       assert(sum === 2)
       assert(sum + 2 === 4)
     }

   it must "subtract correctly" taggedAs(SlowTest, DbTest) in {
     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 "The Scala language should subtract correctly" with the com.mycompany.groups.DbTest tag.

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

Ignored tests

 import org.scalatest.FlatSpec
 import scala.collection.mutable.Stack

 class StackSpec extends FlatSpec {

   "A Stack" should "pop values in last-in-first-out order" in {
       val stack = new Stack[Int]
       stack.push(1)
       stack.push(2)
       assert(stack.pop() === 2)
       assert(stack.pop() === 1)
     }

   ignore should "throw NoSuchElementException if an empty stack is popped" in {
     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 first test and report that the second test was ignored:

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

When using shorthand notation, you won't have an it to change into ignore for the first test of each new subject. To ignore such tests, you must instead change in to ignore. For example, to temporarily disable the test with the name "A Stack should pop values in last-in-first-out order", change “in” into “ignore” like this:

 import org.scalatest.FlatSpec
 import scala.collection.mutable.Stack

 class StackSpec extends FlatSpec {

   "A Stack" should "pop values in last-in-first-out order" ignore {
       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" in {
     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
 

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

 import org.scalatest.FlatSpec

 class ArithmeticSpec extends FlatSpec {

  "The Scala language" must "add correctly" in {
     val sum = 2 + 3
     assert(sum === 5)
     info("addition seems to work")
   }

   it must "subtract correctly" in {
     val diff = 7 - 2
     assert(diff === 5)
   }
 }
 

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

 scala> (new ArithmeticSpec).execute()
 The Scala language 
 - must add correctly
   + addition seems to work 
 - must subtract correctly
 

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

 import org.scalatest.FlatSpec
 import org.scalatest.GivenWhenThen
 
 class ArithmeticSpec extends FlatSpec with GivenWhenThen {
 
  "The Scala language" must "add correctly" in { 
 
     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)
   }
 
   it must "subtract correctly" in {
 
     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)
   }
 }
 

 scala> (new ArithmeticSpec).execute()
 The Scala language 
 - must add correctly
   + Given two integers 
   + When they are added 
   + Then the result is the sum of the two numbers 
 - must subtract correctly
   + 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 it is intended to test, has not yet been implemented. You can mark tests as pending in FlatSpec like this:

 import org.scalatest.FlatSpec

 class ArithmeticSpec extends FlatSpec {

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

  "The Scala language" must "add correctly" in {
     val sum = 2 + 3
     assert(sum === shared)
   }

   it must "subtract correctly" is (pending)
 }
 

If you run this version of ArithmeticSpec with:

 scala> (new ArithmeticSpec).execute()
 

It will run both tests but report that The Scala language must subtract correctly is pending. You'll see:

 The Scala language
 - must add correctly
 - must subtract correctly (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 FlatSpec:

  "The Scala language" must "add correctly" in { 
     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:

 The Scala language
 - must add correctly (pending)
   + Given two integers 
   + When they are added 
   + Then the result is the sum of the two numbers