trait Checkers extends ScalaCheckConfiguration

Trait that contains several “check” methods that perform ScalaCheck property checks. If ScalaCheck finds a test case for which a property doesn't hold, the problem will be reported as a ScalaTest test failure.

To use ScalaCheck, you specify properties and, in some cases, generators that generate test data. You need not always create generators, because ScalaCheck provides many default generators for you that can be used in many situations. ScalaCheck will use the generators to generate test data and with that data run tests that check that the property holds. Property-based tests can, therefore, give you a lot more testing for a lot less code than assertion-based tests. Here's an example of using ScalaCheck from a JUnitSuite:

import org.scalatest.junit.JUnitSuite
import org.scalatest.prop.Checkers
import org.scalacheck.Arbitrary._
import org.scalacheck.Prop._

class MySuite extends JUnitSuite with Checkers {
  @Test
  def testConcat() {
    check((a: List[Int], b: List[Int]) => a.size + b.size == (a ::: b).size)
  }
}

The check method, defined in Checkers, makes it easy to write property-based tests inside ScalaTest, JUnit, and TestNG test suites. This example specifies a property that List's ::: method should obey. ScalaCheck properties are expressed as function values that take the required test data as parameters. ScalaCheck will generate test data using generators and repeatedly pass generated data to the function. In this case, the test data is composed of integer lists named a and b. Inside the body of the function, you see:

a.size + b.size == (a ::: b).size

The property in this case is a Boolean expression that will yield true if the size of the concatenated list is equal to the size of each individual list added together. With this small amount of code, ScalaCheck will generate possibly hundreds of value pairs for a and b and test each pair, looking for a pair of integers for which the property doesn't hold. If the property holds true for every value ScalaCheck tries, check returns normally. Otherwise, check will complete abruptly with a TestFailedException that contains information about the failure, including the values that cause the property to be false.

For more information on using ScalaCheck properties, see the documentation for ScalaCheck, which is available from http://code.google.com/p/scalacheck/.

To execute a suite that mixes in Checkers with ScalaTest's Runner, you must include ScalaCheck's jar file on the class path or runpath.

Property check configuration

The property checks performed by the check methods of this trait can be flexibly configured via the services provided by supertrait Configuration. The five configuration parameters for property checks along with their default values and meanings are described in the following table:

Configuration Parameter Default Value Meaning
minSuccessful 100 the minimum number of successful property evaluations required for the property to pass
maxDiscarded 500 the maximum number of discarded property evaluations allowed during a property check
minSize 0 the minimum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists)
maxSize 100 the maximum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists)
workers 1 specifies the number of worker threads to use during property evaluation

The check methods of trait Checkers each take a PropertyCheckConfiguration object as an implicit parameter. This object provides values for each of the five configuration parameters. Trait Configuration provides an implicit val named generatorDrivenConfig with each configuration parameter set to its default value. If you want to set one or more configuration parameters to a different value for all property checks in a suite you can override this val (or hide it, for example, if you are importing the members of the Checkers companion object rather than mixing in the trait.) For example, if you want all parameters at their defaults except for minSize and maxSize, you can override generatorDrivenConfig, like this:

implicit override val generatorDrivenConfig =
  PropertyCheckConfiguration(minSize = 10, sizeRange = 10)

Or, if hide it by declaring a variable of the same name in whatever scope you want the changed values to be in effect:

implicit val generatorDrivenConfig =
  PropertyCheckConfiguration(minSize = 10, sizeRange = 10)

In addition to taking a PropertyCheckConfiguration object as an implicit parameter, the check methods of trait Checkers also take a variable length argument list of PropertyCheckConfigParam objects that you can use to override the values provided by the implicit PropertyCheckConfiguration for a single check invocation. You place these configuration settings after the property or property function, For example, if you want to set minSuccessful to 500 for just one particular check invocation, you can do so like this:

check((n: Int) => n + 0 == n, minSuccessful(500))

This invocation of check will use 500 for minSuccessful and whatever values are specified by the implicitly passed PropertyCheckConfiguration object for the other configuration parameters. If you want to set multiple configuration parameters in this way, just list them separated by commas:

check((n: Int) => n + 0 == n, minSuccessful(500), maxDiscardedFactor(0.6))

The previous configuration approach works the same in Checkers as it does in GeneratorDrivenPropertyChecks. Trait Checkers also provides one check method that takes an org.scalacheck.Test.Parameters object, in case you want to configure ScalaCheck that way.

import org.scalacheck.Prop
import org.scalacheck.Test.Parameters
import org.scalatest.prop.Checkers._

check(Prop.forAll((n: Int) => n + 0 == n), Parameters.Default { override val minSuccessfulTests = 5 })

For more information, see the documentation for supertrait Configuration.

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Type Members

  1. case class MaxDiscardedFactor extends PropertyCheckConfigParam with Product with Serializable
    Definition Classes
    Configuration
  2. case class MinSize extends PropertyCheckConfigParam with Product with Serializable
    Definition Classes
    Configuration
  3. case class MinSuccessful extends PropertyCheckConfigParam with Product with Serializable
    Definition Classes
    Configuration
  4. sealed abstract class PropertyCheckConfigParam extends Product with Serializable
    Definition Classes
    Configuration
  5. case class PropertyCheckConfiguration extends Product with Serializable
    Definition Classes
    Configuration
  6. case class SizeRange extends PropertyCheckConfigParam with Product with Serializable
    Definition Classes
    Configuration
  7. case class Workers extends PropertyCheckConfigParam with Product with Serializable
    Definition Classes
    Configuration

Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##(): Int
    Definition Classes
    AnyRef → Any
  3. final def ==(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  4. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  5. def check(p: Prop, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfiguration, prettifier: Prettifier, pos: Position): Assertion

    Check a property.

    Check a property.

    p

    the property to check

    Exceptions thrown

    TestFailedException if a test case is discovered for which the property doesn't hold.

  6. def check(p: Prop, prms: Parameters)(implicit prettifier: Prettifier, pos: Position): Assertion

    Check a property with the given testing parameters.

    Check a property with the given testing parameters.

    p

    the property to check

    prms

    the test parameters

    Exceptions thrown

    TestFailedException if a test case is discovered for which the property doesn't hold.

  7. def check[A1, A2, A3, A4, A5, A6, P](f: (A1, A2, A3, A4, A5, A6) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfiguration, p: (P) ⇒ Prop, a1: Arbitrary[A1], s1: Shrink[A1], pp1: (A1) ⇒ Pretty, a2: Arbitrary[A2], s2: Shrink[A2], pp2: (A2) ⇒ Pretty, a3: Arbitrary[A3], s3: Shrink[A3], pp3: (A3) ⇒ Pretty, a4: Arbitrary[A4], s4: Shrink[A4], pp4: (A4) ⇒ Pretty, a5: Arbitrary[A5], s5: Shrink[A5], pp5: (A5) ⇒ Pretty, a6: Arbitrary[A6], s6: Shrink[A6], pp6: (A6) ⇒ Pretty, prettifier: Prettifier, pos: Position): Assertion

    Convert the passed 6-arg function into a property, and check it.

    Convert the passed 6-arg function into a property, and check it.

    f

    the function to be converted into a property and checked

    Exceptions thrown

    TestFailedException if a test case is discovered for which the property doesn't hold.

  8. def check[A1, A2, A3, A4, A5, P](f: (A1, A2, A3, A4, A5) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfiguration, p: (P) ⇒ Prop, a1: Arbitrary[A1], s1: Shrink[A1], pp1: (A1) ⇒ Pretty, a2: Arbitrary[A2], s2: Shrink[A2], pp2: (A2) ⇒ Pretty, a3: Arbitrary[A3], s3: Shrink[A3], pp3: (A3) ⇒ Pretty, a4: Arbitrary[A4], s4: Shrink[A4], pp4: (A4) ⇒ Pretty, a5: Arbitrary[A5], s5: Shrink[A5], pp5: (A5) ⇒ Pretty, prettifier: Prettifier, pos: Position): Assertion

    Convert the passed 5-arg function into a property, and check it.

    Convert the passed 5-arg function into a property, and check it.

    f

    the function to be converted into a property and checked

    Exceptions thrown

    TestFailedException if a test case is discovered for which the property doesn't hold.

  9. def check[A1, A2, A3, A4, P](f: (A1, A2, A3, A4) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfiguration, p: (P) ⇒ Prop, a1: Arbitrary[A1], s1: Shrink[A1], pp1: (A1) ⇒ Pretty, a2: Arbitrary[A2], s2: Shrink[A2], pp2: (A2) ⇒ Pretty, a3: Arbitrary[A3], s3: Shrink[A3], pp3: (A3) ⇒ Pretty, a4: Arbitrary[A4], s4: Shrink[A4], pp4: (A4) ⇒ Pretty, prettifier: Prettifier, pos: Position): Assertion

    Convert the passed 4-arg function into a property, and check it.

    Convert the passed 4-arg function into a property, and check it.

    f

    the function to be converted into a property and checked

    Exceptions thrown

    TestFailedException if a test case is discovered for which the property doesn't hold.

  10. def check[A1, A2, A3, P](f: (A1, A2, A3) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfiguration, p: (P) ⇒ Prop, a1: Arbitrary[A1], s1: Shrink[A1], pp1: (A1) ⇒ Pretty, a2: Arbitrary[A2], s2: Shrink[A2], pp2: (A2) ⇒ Pretty, a3: Arbitrary[A3], s3: Shrink[A3], pp3: (A3) ⇒ Pretty, prettifier: Prettifier, pos: Position): Assertion

    Convert the passed 3-arg function into a property, and check it.

    Convert the passed 3-arg function into a property, and check it.

    f

    the function to be converted into a property and checked

    Exceptions thrown

    TestFailedException if a test case is discovered for which the property doesn't hold.

  11. def check[A1, A2, P](f: (A1, A2) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfiguration, p: (P) ⇒ Prop, a1: Arbitrary[A1], s1: Shrink[A1], pp1: (A1) ⇒ Pretty, a2: Arbitrary[A2], s2: Shrink[A2], pp2: (A2) ⇒ Pretty, prettifier: Prettifier, pos: Position): Assertion

    Convert the passed 2-arg function into a property, and check it.

    Convert the passed 2-arg function into a property, and check it.

    f

    the function to be converted into a property and checked

    Exceptions thrown

    TestFailedException if a test case is discovered for which the property doesn't hold.

  12. def check[A1, P](f: (A1) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfiguration, p: (P) ⇒ Prop, a1: Arbitrary[A1], s1: Shrink[A1], pp1: (A1) ⇒ Pretty, prettifier: Prettifier, pos: Position): Assertion

    Convert the passed 1-arg function into a property, and check it.

    Convert the passed 1-arg function into a property, and check it.

    f

    the function to be converted into a property and checked

    Exceptions thrown

    TestFailedException if a test case is discovered for which the property doesn't hold.

  13. def clone(): AnyRef
    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @native() @throws( ... )
  14. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  15. def equals(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  16. def finalize(): Unit
    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( classOf[java.lang.Throwable] )
  17. implicit val generatorDrivenConfig: PropertyCheckConfiguration
    Definition Classes
    Configuration
  18. final def getClass(): Class[_]
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  19. def getParameter(configParams: Seq[PropertyCheckConfigParam], config: PropertyCheckConfiguration): Parameter
    Definition Classes
    Configuration
  20. def hashCode(): Int
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  21. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  22. def maxDiscardedFactor(value: PosZDouble): MaxDiscardedFactor
    Definition Classes
    Configuration
  23. def minSize(value: PosZInt): MinSize
    Definition Classes
    Configuration
  24. def minSuccessful(value: PosInt): MinSuccessful
    Definition Classes
    Configuration
  25. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  26. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  27. final def notifyAll(): Unit
    Definition Classes
    AnyRef
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    @native()
  28. def sizeRange(value: PosZInt): SizeRange
    Definition Classes
    Configuration
  29. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  30. def toString(): String
    Definition Classes
    AnyRef → Any
  31. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  32. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  33. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @native() @throws( ... )
  34. def workers(value: PosInt): Workers
    Definition Classes
    Configuration

Inherited from ScalaCheckConfiguration

Inherited from Configuration

Inherited from AnyRef

Inherited from Any

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