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 ParameterDefault ValueMeaning
minSuccessful100the minimum number of successful property evaluations required for the property to pass
maxDiscarded500the maximum number of discarded property evaluations allowed during a property check
minSize0the minimum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists)
maxSize100the maximum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists)
workers1specifies the number of worker threads to use during property evaluation

The check methods of trait Checkers each take a PropertyCheckConfigobject as an implicit parameter. This object provides values for each of the five configuration parameters. Trait Configurationprovides 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 overridegeneratorDrivenConfig, 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 traitCheckers also take a variable length argument list of PropertyCheckConfigParamobjects that you can use to override the values provided by the implicit PropertyCheckConfig for a single checkinvocation. 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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known subclasses: Checkers
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Type Members

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

    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

    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

    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

    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

    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

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

Value Members

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

    attributes: final
    definition classes: AnyRef
  2. def != (arg0: Any) : Boolean

    o != arg0 is the same as !(o == (arg0)).

    o != arg0 is the same as !(o == (arg0)).

    arg0

    the object to compare against this object for dis-equality.

    returns

    false if the receiver object is equivalent to the argument; true otherwise.

    attributes: final
    definition classes: Any
  3. def ## () : Int

    attributes: final
    definition classes: AnyRef → Any
  4. def $asInstanceOf [T0] () : T0

    attributes: final
    definition classes: AnyRef
  5. def $isInstanceOf [T0] () : Boolean

    attributes: final
    definition classes: AnyRef
  6. def == (arg0: AnyRef) : Boolean

    o == arg0 is the same as if (o eq null) arg0 eq null else o.equals(arg0).

    o == arg0 is the same as if (o eq null) arg0 eq null else o.equals(arg0).

    arg0

    the object to compare against this object for equality.

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    attributes: final
    definition classes: AnyRef
  7. def == (arg0: Any) : Boolean

    o == arg0 is the same as o.equals(arg0).

    o == arg0 is the same as o.equals(arg0).

    arg0

    the object to compare against this object for equality.

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    attributes: final
    definition classes: Any
  8. def asInstanceOf [T0] : T0

    This method is used to cast the receiver object to be of type T0.

    This method is used to cast the receiver object to be of type T0.

    Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expressionList(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested typed.

    returns

    the receiver object.

    attributes: final
    definition classes: Any
  9. def check (p: Prop, configParams: PropertyCheckConfigParam*)(implicit config: PropertyCheckConfig) : Unit

    Check a property.

    Check a property.

    p

    the property to check

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. def clone () : AnyRef

    This method creates and returns a copy of the receiver object.

    This method creates and returns a copy of the receiver object.

    The default implementation of the clone method is platform dependent.

    returns

    a copy of the receiver object.

    attributes: protected
    definition classes: AnyRef
  18. def eq (arg0: AnyRef) : Boolean

    This method is used to test whether the argument (arg0) is a reference to the receiver object (this).

    This method is used to test whether the argument (arg0) is a reference to the receiver object (this).

    The eq method implements an [http://en.wikipedia.org/wiki/Equivalence_relation equivalence relation] on non-null instances of AnyRef: * It is reflexive: for any non-null instance x of type AnyRef, x.eq(x) returns true. * It is symmetric: for any non-null instances x and y of type AnyRef, x.eq(y) returns true if and only if y.eq(x) returns true. * It is transitive: for any non-null instances x, y, and z of type AnyRef if x.eq(y) returns true and y.eq(z) returns true, then x.eq(z) returns true.

    Additionally, the eq method has three other properties. * It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false. * For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false. * null.eq(null) returns true.

    When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).

    arg0

    the object to compare against this object for reference equality.

    returns

    true if the argument is a reference to the receiver object; false otherwise.

    attributes: final
    definition classes: AnyRef
  19. def equals (arg0: Any) : Boolean

    This method is used to compare the receiver object (this) with the argument object (arg0) for equivalence.

    This method is used to compare the receiver object (this) with the argument object (arg0) for equivalence.

    The default implementations of this method is an [http://en.wikipedia.org/wiki/Equivalence_relation equivalence relation]: * It is reflexive: for any instance x of type Any, x.equals(x) should return true. * It is symmetric: for any instances x and y of type Any, x.equals(y) should return true if and only if y.equals(x) returns true. * It is transitive: for any instances x, y, and z of type AnyRef if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.

    If you override this method, you should verify that your implementation remains an equivalence relation. Additionally, when overriding this method it is often necessary to override hashCode to ensure that objects that are "equal" (o1.equals(o2) returns true) hash to the same scala.Int (o1.hashCode.equals(o2.hashCode)).

    arg0

    the object to compare against this object for equality.

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    definition classes: AnyRef → Any
  20. def finalize () : Unit

    This method is called by the garbage collector on the receiver object when garbage collection determines that there are no more references to the object.

    This method is called by the garbage collector on the receiver object when garbage collection determines that there are no more references to the object.

    The details of when and if the finalize method are invoked, as well as the interaction between finalizeand non-local returns and exceptions, are all platform dependent.

    attributes: protected
    definition classes: AnyRef
  21. implicit val generatorDrivenConfig : PropertyCheckConfig

    Implicit PropertyCheckConfig value providing default configuration values.

    Implicit PropertyCheckConfig value providing default configuration values.

    attributes: implicit
    definition classes: Configuration
  22. def getClass () : java.lang.Class[_]

    Returns a representation that corresponds to the dynamic class of the receiver object.

    Returns a representation that corresponds to the dynamic class of the receiver object.

    The nature of the representation is platform dependent.

    returns

    a representation that corresponds to the dynamic class of the receiver object.

    attributes: final
    definition classes: AnyRef
  23. def hashCode () : Int

    Returns a hash code value for the object.

    Returns a hash code value for the object.

    The default hashing algorithm is platform dependent.

    Note that it is allowed for two objects to have identical hash codes (o1.hashCode.equals(o2.hashCode)) yet not be equal (o1.equals(o2) returns false). A degenerate implementation could always return 0. However, it is required that if two objects are equal (o1.equals(o2) returns true) that they have identical hash codes (o1.hashCode.equals(o2.hashCode)). Therefore, when overriding this method, be sure to verify that the behavior is consistent with the equals method.

    returns

    the hash code value for the object.

    definition classes: AnyRef → Any
  24. def isInstanceOf [T0] : Boolean

    This method is used to test whether the dynamic type of the receiver object is T0.

    This method is used to test whether the dynamic type of the receiver object is T0.

    Note that the test result of the test is modulo Scala's erasure semantics. Therefore the expression1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested typed.

    returns

    true if the receiver object is an instance of erasure of type T0; false otherwise.

    attributes: final
    definition classes: Any
  25. 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
  26. 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
  27. 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
  28. 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
  29. def ne (arg0: AnyRef) : Boolean

    o.ne(arg0) is the same as !(o.eq(arg0)).

    o.ne(arg0) is the same as !(o.eq(arg0)).

    arg0

    the object to compare against this object for reference dis-equality.

    returns

    false if the argument is not a reference to the receiver object; true otherwise.

    attributes: final
    definition classes: AnyRef
  30. def notify () : Unit

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Wakes up a single thread that is waiting on the receiver object's monitor.

    attributes: final
    definition classes: AnyRef
  31. def notifyAll () : Unit

    Wakes up all threads that are waiting on the receiver object's monitor.

    Wakes up all threads that are waiting on the receiver object's monitor.

    attributes: final
    definition classes: AnyRef
  32. def synchronized [T0] (arg0: T0) : T0

    attributes: final
    definition classes: AnyRef
  33. def toString () : String

    Returns a string representation of the object.

    Returns a string representation of the object.

    The default representation is platform dependent.

    returns

    a string representation of the object.

    definition classes: AnyRef → Any
  34. def wait () : Unit

    attributes: final
    definition classes: AnyRef
  35. def wait (arg0: Long, arg1: Int) : Unit

    attributes: final
    definition classes: AnyRef
  36. def wait (arg0: Long) : Unit

    attributes: final
    definition classes: AnyRef
  37. 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