org.scalatest.prop

Checkers

trait Checkers extends AnyRef

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. 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.

Inherits

  1. AnyRef
  2. Any

Value Members

  1. def check(p: Prop): Unit

    Check a property

    Check a property.

    p

    the property to check

  2. 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

  3. def check[A1, A2, A3, A4, A5, A6, P](f: (A1, A2, A3, A4, A5, A6) ⇒ P)(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

  4. def check[A1, A2, A3, A4, A5, P](f: (A1, A2, A3, A4, A5) ⇒ P)(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

  5. def check[A1, A2, A3, A4, P](f: (A1, A2, A3, A4) ⇒ P)(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

  6. def check[A1, A2, A3, P](f: (A1, A2, A3) ⇒ P)(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

  7. def check[A1, A2, P](f: (A1, A2) ⇒ P)(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

  8. def check[A1, P](f: (A1) ⇒ P)(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

  9. 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 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 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
  10. 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.

    definition classes: AnyRef ⇐ Any
  11. def toString(): String

    Returns a string representation of the object

    Returns a string representation of the object.

    The default representation is platform dependent.

    definition classes: AnyRef ⇐ Any