org.scalatest.prop

# Checkers

#### trait Checkers extends AnyRef

Trait that contains several &#8220;check&#8221; 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. This version of `Checkers` was tested with ScalaCheck version 1.1.1. This trait must be mixed into a ScalaTest `Suite`, because its self type is `org.scalatest.Suite`.

authors:

1. Bill Venners

Inherited

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Visibility

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### 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 expression`1.asInstanceOf[String]` will throw a `ClassCastException` at runtime, while the expression`List(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): 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)(implicit 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)(implicit 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)(implicit 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)(implicit 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)(implicit 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)(implicit 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 `finalize`and non-local returns and exceptions, are all platform dependent.

    attributes: protected
    definition classes: AnyRef

21. #### def getClass(): java.lang.Class[_ <: java.lang.Object]

    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

22. #### 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

23. #### 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 expression`1.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

24. #### 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

25. #### 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

26. #### 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

27. #### def synchronized[T0](arg0: T0): T0

    attributes: final
    definition classes: AnyRef

28. #### 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

29. #### def wait(): Unit

    attributes: final
    definition classes: AnyRef

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

    attributes: final
    definition classes: AnyRef

31. #### def wait(arg0: Long): Unit

    attributes: final
    definition classes: AnyRef