org.scalatest.prop

Checkers

trait Checkers extends Configuration

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 PropertyCheckConfig 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 =
  PropertyCheckConfig(minSize = 10, maxSize = 20)

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 =
  PropertyCheckConfig(minSize = 10, maxSize = 20)

In addition to taking a PropertyCheckConfig 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 PropertyCheckConfig 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 PropertyCheckConfig 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), maxDiscarded(300))

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.Params object, in case you want to configure ScalaCheck that way.

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

check(Prop.forAll((n: Int) => n + 0 == n), Params(minSuccessfulTests = 5))

For more information, see the documentation for supertrait Configuration.

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Type Members

  1. case class MaxDiscarded (value: Int) extends PropertyCheckConfigParam with Product with Serializable

    A PropertyCheckConfigParam that specifies the maximum number of discarded property evaluations allowed during property evaluation.

  2. case class MaxSize (value: Int) extends PropertyCheckConfigParam with Product with Serializable

    A PropertyCheckConfigParam that specifies the maximum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists).

  3. case class MinSize (value: Int) extends PropertyCheckConfigParam with Product with Serializable

    A PropertyCheckConfigParam that specifies the minimum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists).

  4. case class MinSuccessful (value: Int) extends PropertyCheckConfigParam with Product with Serializable

    A PropertyCheckConfigParam that specifies the minimum number of successful property evaluations required for the property to pass.

  5. case class PropertyCheckConfig (minSuccessful: Int, maxDiscarded: Int, minSize: Int, maxSize: Int, workers: Int) extends Product with Serializable

    Configuration object for property checks.

  6. class PropertyCheckConfigParam extends AnyRef

    Abstract class defining a family of configuration parameters for property checks.

  7. case class Workers (value: Int) extends PropertyCheckConfigParam with Product with Serializable

    A PropertyCheckConfigParam that specifies the number of worker threads to use when evaluating a property.

Value Members

  1. def != (arg0: AnyRef): Boolean

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  2. def != (arg0: Any): Boolean

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  3. def ## (): Int

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  4. def == (arg0: AnyRef): Boolean

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  5. def == (arg0: Any): Boolean

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  6. object MaxDiscarded extends AbstractFunction1[Int, MaxDiscarded] with Serializable

  7. object MaxSize extends AbstractFunction1[Int, MaxSize] with Serializable

  8. object MinSize extends AbstractFunction1[Int, MinSize] with Serializable

  9. object MinSuccessful extends AbstractFunction1[Int, MinSuccessful] with Serializable

  10. object PropertyCheckConfig extends AbstractFunction5[Int, Int, Int, Int, Int, PropertyCheckConfig] with Serializable

  11. object Workers extends AbstractFunction1[Int, Workers] with Serializable

  12. def asInstanceOf [T0] : T0

    Attributes
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  13. def check (p: Prop, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfig): Unit

    Check a property.

    Check a property.

    p

    the property to check

  14. def check (p: Prop, prms: Params): Unit

    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

  15. def check [A1, A2, A3, A4, A5, A6, P] (f: (A1, A2, A3, A4, A5, A6) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfig, 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): Unit

    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

  16. def check [A1, A2, A3, A4, A5, P] (f: (A1, A2, A3, A4, A5) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfig, 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): Unit

    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

  17. def check [A1, A2, A3, A4, P] (f: (A1, A2, A3, A4) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfig, 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): Unit

    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

  18. def check [A1, A2, A3, P] (f: (A1, A2, A3) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfig, 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): Unit

    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

  19. def check [A1, A2, P] (f: (A1, A2) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfig, p: (P) ⇒ Prop, a1: Arbitrary[A1], s1: Shrink[A1], pp1: (A1) ⇒ Pretty, a2: Arbitrary[A2], s2: Shrink[A2], pp2: (A2) ⇒ Pretty): Unit

    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

  20. def check [A1, P] (f: (A1) ⇒ P, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfig, p: (P) ⇒ Prop, a1: Arbitrary[A1], s1: Shrink[A1], pp1: (A1) ⇒ Pretty): Unit

    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

  21. def clone (): AnyRef

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  22. def eq (arg0: AnyRef): Boolean

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  23. def equals (arg0: Any): Boolean

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  24. def finalize (): Unit

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  25. implicit val generatorDrivenConfig : PropertyCheckConfig

    Implicit PropertyCheckConfig value providing default configuration values.

    Implicit PropertyCheckConfig value providing default configuration values.

    Attributes
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  26. def getClass (): java.lang.Class[_]

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  27. def hashCode (): Int

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  28. def isInstanceOf [T0] : Boolean

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  29. def maxDiscarded (value: Int): MaxDiscarded

    Returns a MaxDiscarded property check configuration parameter containing the passed value, which specifies the maximum number of discarded property evaluations allowed during property evaluation.

    Returns a MaxDiscarded property check configuration parameter containing the passed value, which specifies the maximum number of discarded property evaluations allowed during property evaluation.

    Definition Classes
    Configuration
  30. def maxSize (value: Int): MaxSize

    Returns a MaxSize property check configuration parameter containing the passed value, which specifies the maximum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists).

    Returns a MaxSize property check configuration parameter containing the passed value, which specifies the maximum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists).

    Note that the maximum size should be greater than or equal to the minimum size. This requirement is enforced by the PropertyCheckConfig constructor and the forAll methods of traits PropertyChecks and Checkers. In other words, it is enforced at the point both a maximum and minimum size are provided together.

    Definition Classes
    Configuration
  31. def minSize (value: Int): MinSize

    Returns a MinSize property check configuration parameter containing the passed value, which specifies the minimum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists).

    Returns a MinSize property check configuration parameter containing the passed value, which specifies the minimum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists).

    Definition Classes
    Configuration
  32. def minSuccessful (value: Int): MinSuccessful

    Returns a MinSuccessful property check configuration parameter containing the passed value, which specifies the minimum number of successful property evaluations required for the property to pass.

    Returns a MinSuccessful property check configuration parameter containing the passed value, which specifies the minimum number of successful property evaluations required for the property to pass.

    Definition Classes
    Configuration
  33. def ne (arg0: AnyRef): Boolean

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  34. def notify (): Unit

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  35. def notifyAll (): Unit

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  36. def synchronized [T0] (arg0: ⇒ T0): T0

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  37. def toString (): String

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  38. def wait (): Unit

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  39. def wait (arg0: Long, arg1: Int): Unit

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  40. def wait (arg0: Long): Unit

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  41. def workers (value: Int): Workers

    Returns a Workers property check configuration parameter containing the passed value, which specifies the number of worker threads to use when evaluating a property.

    Returns a Workers property check configuration parameter containing the passed value, which specifies the number of worker threads to use when evaluating a property.

    Definition Classes
    Configuration

Inherited from Configuration

Inherited from AnyRef

Inherited from Any