AnyPropSpec

A suite of property-based tests.

Here's an example AnyPropSpec:

package org.scalatest.examples.propspec

import org.scalatest._
import prop._
import scala.collection.immutable._

class SetSpec extends propspec.AnyPropSpec with TableDrivenPropertyChecks with Matchers {

  val examples =
    Table(
      "set",
      BitSet.empty,
      HashSet.empty[Int],
      TreeSet.empty[Int]
    )

  property("an empty Set should have size 0") {
    forAll(examples) { set =>
      set.size should be (0)
    }
  }

  property("invoking head on an empty set should produce NoSuchElementException") {
    forAll(examples) { set =>
      a [NoSuchElementException] should be thrownBy { set.head }
    }
  }
}

You can run a AnyPropSpec by invoking execute on it. This method, which prints test results to the standard output, is intended to serve as a convenient way to run tests from within the Scala interpreter. For example, to run SetSpec from within the Scala interpreter, you could write:

scala> org.scalatest.run(new SetSpec)

And you would see:

SetSpec:
- an empty Set should have size 0
- invoking head on an empty Set should produce NoSuchElementException

Or, to run just the “an empty Set should have size 0” method, 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 SetSpec, "size 0")
SetSpec:
- an empty Set 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 execute (below) and 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.

“property” is a method, defined in AnyPropSpec, which will be invoked by the primary constructor of SetSpec. You specify the name of the test as a string between the parentheses, and the test code itself between curly braces. The test code is a function passed as a by-name parameter to property, which registers it for later execution.

A AnyPropSpec'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 with the property method while the AnyPropSpec is in its registration phase. Any attempt to register a test after the AnyPropSpec has entered its ready phase, i.e., after run has been invoked on the AnyPropSpec, will be met with a thrown TestRegistrationClosedException. The recommended style of using AnyPropSpec 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.

Ignored tests

To support the common use case of temporarily disabling a test, with the good intention of resurrecting the test at a later time, AnyPropSpec provides registration methods that start with ignore instead of property. Here's an example:

package org.scalatest.examples.suite.ignore

import org.scalatest._
import prop._
import scala.collection.immutable._

class SetSpec extends propspec.AnyPropSpec with TableDrivenPropertyChecks with Matchers {

  val examples =
    Table(
      "set",
      BitSet.empty,
      HashSet.empty[Int],
      TreeSet.empty[Int]
    )

  ignore("an empty Set should have size 0") {
    forAll(examples) { set =>
      set.size should be (0)
    }
  }

  property("invoking head on an empty set should produce NoSuchElementException") {
    forAll(examples) { set =>
      a [NoSuchElementException] should be thrownBy { set.head }
    }
  }
}

If you run this version of SetSuite with:

scala> org.scalatest.run(new SetSpec)

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

SetSuite:
- an empty Set should have size 0 !!! IGNORED !!!
- invoking head on an empty Set should produce NoSuchElementException

Informers

One of the parameters to AnyPropSpec'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 AnyPropSpec'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 that shows both a direct use as well as an indirect use through the methods of GivenWhenThen:

package org.scalatest.examples.propspec.info

import org.scalatest._
import prop._
import collection.mutable

class SetSpec extends propspec.AnyPropSpec with TableDrivenPropertyChecks with GivenWhenThen {

  val examples =
    Table(
      "set",
      mutable.BitSet.empty,
      mutable.HashSet.empty[Int],
      mutable.LinkedHashSet.empty[Int]
    )

  property("an element can be added to an empty mutable Set") {

    forAll(examples) { set =>

      info("----------------")

      Given("an empty mutable " + set.getClass.getSimpleName)
      assert(set.isEmpty)

      When("an element is added")
      set += 99

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

      And("the Set should contain the added element")
      assert(set.contains(99))
    }
  }
}

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

scala> org.scalatest.run(new SetSpec)
SetSpec:
- an element can be added to an empty mutable Set
  + ----------------
  + Given an empty mutable BitSet
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + ----------------
  + Given an empty mutable HashSet
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element
  + ----------------
  + Given an empty mutable LinkedHashSet
  + When an element is added
  + Then the Set should have size 1
  + And the Set should contain the added element

Documenters

AnyPropSpec 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 AnyPropSpec that uses markup:

package org.scalatest.examples.propspec.markup

import org.scalatest._
import prop._
import collection.mutable

class SetSpec extends propspec.AnyPropSpec with TableDrivenPropertyChecks 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.

  """ }

  val examples =
    Table(
      "set",
      mutable.BitSet.empty,
      mutable.HashSet.empty[Int],
      mutable.LinkedHashSet.empty[Int]
    )

  property("an element can be added to an empty mutable Set") {

    forAll(examples) { set =>

      info("----------------")

      Given("an empty mutable " + set.getClass.getSimpleName)
      assert(set.isEmpty)

      When("an element is added")
      set += 99

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

      And("the Set should contain the added element")
      assert(set.contains(99))
    }

    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.propspec.note

import org.scalatest._
import prop._
import collection.mutable

class SetSpec extends propspec.AnyPropSpec with TableDrivenPropertyChecks {

  val examples =
    Table(
      "set",
      mutable.BitSet.empty,
      mutable.HashSet.empty[Int],
      mutable.LinkedHashSet.empty[Int]
    )

  property("an element can be added to an empty mutable Set") {

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

    forAll(examples) { set =>

      assert(set.isEmpty)
      set += 99
      assert(set.size === 1)
      assert(set.contains(99))
    }
  }
}

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:
  + notes are sent immediately
  + alerts are also sent immediately
- an element can be added to an empty mutable Set
  + 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 tests pending in AnyPropSpec like this:

import org.scalatest._
import prop._
import scala.collection.immutable._

class SetSpec extends propspec.AnyPropSpec with TableDrivenPropertyChecks with Matchers {

  val examples =
    Table(
      "set",
      BitSet.empty,
      HashSet.empty[Int],
      TreeSet.empty[Int]
    )

  property("an empty Set should have size 0") (pending)

  property("invoking head on an empty set should produce NoSuchElementException") {
    forAll(examples) { set =>
      a [NoSuchElementException] should be thrownBy { set.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 SetSuite with:

scala> org.scalatest.run(new SetSuite)

It will run both tests, but report that first test is pending. You'll see:

SetSuite:
- An empty Set should have size 0 (pending)
- Invoking head on an empty Set should produce NoSuchElementException

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.

Tagging tests

A AnyPropSpec's tests may be classified into groups by tagging them with string names. As with any suite, when executing a AnyPropSpec, groups of tests can optionally be included and/or excluded. To tag a AnyPropSpec's tests, you pass objects that extend class org.scalatest.Tag to methods that register tests. Class Tag takes one parameter, a string name. If you have created tag annotation interfaces as described in the Tag documentation, then you will probably want to use tag names on your test functions that match. To do so, simply pass the fully qualified names of the tag interfaces to the Tag constructor. For example, if you've defined a tag annotation interface with fully qualified names, com.mycompany.tags.DbTest, then you could create a matching tag for AnyPropSpecs like this:

package org.scalatest.examples.propspec.tagging

import org.scalatest.Tag

object DbTest extends Tag("com.mycompany.tags.DbTest")

Given these definitions, you could place AnyPropSpec tests into groups with tags like this:

import org.scalatest._
import prop._
import tagobjects.Slow
import scala.collection.immutable._

class SetSpec extends propspec.AnyPropSpec with TableDrivenPropertyChecks with Matchers {

  val examples =
    Table(
      "set",
      BitSet.empty,
      HashSet.empty[Int],
      TreeSet.empty[Int]
    )

  property("an empty Set should have size 0", Slow) {
    forAll(examples) { set =>
      set.size should be (0)
    }
  }

  property("invoking head on an empty set should produce NoSuchElementException",
      Slow, DbTest) {

    forAll(examples) { set =>
      a [NoSuchElementException] should be thrownBy { set.head }
    }
  }
}

This code marks both tests with the org.scalatest.tags.Slow tag, and the second test with the com.mycompany.tags.DbTest tag.

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 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.

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 techniques in AnyPropSpec are identical to those in FunSuite, but with “test” replaced by “property”. The following table summarizes the options with a link to the relevant documentation for trait FunSuite:

Using AnyPropSpec to implement a test matrix

Using fixture-context objects in a AnyPropSpec is a good way to implement a test matrix. What is the matrix? A test matrix is a series of tests that you need to run on a series of subjects. For example, The Scala API contains many implementations of trait Set. Every implementation must obey the contract of Set. One property of any Set is that an empty Set should have size 0, another is that invoking head on an empty Set should give you a NoSuchElementException, and so on. Already you have a matrix, where rows are the properties and the columns are the set implementations:

One way to implement this test matrix is to define a trait to represent the columns (in this case, BitSet, HashSet, and TreeSet) as elements in a single-dimensional Table. Each element in the Table represents one Set implementation. Because different properties may require different fixture instances for those implementations, you can define a trait to hold the examples, like this:

trait SetExamples extends Tables {

  def examples = Table("set", bitSet, hashSet, treeSet)

  def bitSet: BitSet
  def hashSet: HashSet[Int]
  def treeSet: TreeSet[Int]
}

Given this trait, you could provide empty sets in one implementation of SetExamples, and non-empty sets in another. Here's how you might provide empty set examples:

class EmptySetExamples extends SetExamples {
  def bitSet = BitSet.empty
  def hashSet = HashSet.empty[Int]
  def treeSet = TreeSet.empty[Int]
}

And here's how you might provide set examples with one item each:

class SetWithOneItemExamples extends SetExamples {
  def bitSet = BitSet(1)
  def hashSet = HashSet(1)
  def treeSet = TreeSet(1)
}

Armed with these example classes, you can define checks of properties that require empty or non-empty set fixtures by using instances of these classes as fixture-context objects. In other words, the columns of the test matrix are implemented as elements of a one-dimensional table of fixtures, the rows are implemented as property clauses of a AnyPropSpec.

Here's a complete example that checks the two properties mentioned previously:

package org.scalatest.examples.propspec.matrix

import org.scalatest._
import org.scalatest.prop._
import scala.collection.immutable._

trait SetExamples extends Tables {

  def examples = Table("set", bitSet, hashSet, treeSet)

  def bitSet: BitSet
  def hashSet: HashSet[Int]
  def treeSet: TreeSet[Int]
}

class EmptySetExamples extends SetExamples {
  def bitSet = BitSet.empty
  def hashSet = HashSet.empty[Int]
  def treeSet = TreeSet.empty[Int]
}

class SetSpec extends propspec.AnyPropSpec with TableDrivenPropertyChecks with Matchers {

  property("an empty Set should have size 0") {
    new EmptySetExamples {
      forAll(examples) { set =>
        set.size should be (0)
      }
    }
  }

  property("invoking head on an empty set should produce NoSuchElementException") {
    new EmptySetExamples {
      forAll(examples) { set =>
        a [NoSuchElementException] should be thrownBy { set.head }
      }
    }
  }
}

One benefit of this approach is that the compiler will help you when you need to add either a new row or column to the matrix. In either case, you'll need to ensure all cells are checked to get your code to compile.

Shared tests

Sometimes you may want to run the same test code on different fixture objects. That is to say, you may want to write tests that are "shared" by different fixture objects. You accomplish this in a AnyPropSpec in the same way you would do it in a FunSuite, except instead of test you say property, and instead of testsFor you say propertiesFor. For more information, see the Shared tests section of FunSuite's documentation.