org.scalatest.prop

Whenever

trait Whenever extends AnyRef

Trait that contains the whenever clause that can be used in table- or generator-driven property checks.

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  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. def asInstanceOf [T0] : T0

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  7. def clone (): AnyRef

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  8. def eq (arg0: AnyRef): Boolean

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  9. def equals (arg0: Any): Boolean

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  10. def finalize (): Unit

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

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  13. def isInstanceOf [T0] : Boolean

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  14. def ne (arg0: AnyRef): Boolean

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  15. def notify (): Unit

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  16. def notifyAll (): Unit

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

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  18. def toString (): String

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  19. def wait (): Unit

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

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  21. def wait (arg0: Long): Unit

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  22. def whenever (condition: Boolean)(fun: ⇒ Unit): Unit

    Evaluates the passed code block if the passed boolean condition is true, else throws DiscardedEvaluationException.

    Evaluates the passed code block if the passed boolean condition is true, else throws DiscardedEvaluationException.

    The whenever method can be used inside property check functions to discard invocations of the function with data for which it is known the property would fail. For example, given the following Fraction class:

    class Fraction(n: Int, d: Int) {
    
      require(d != 0)
      require(d != Integer.MIN_VALUE)
      require(n != Integer.MIN_VALUE)
    
      val numer = if (d < 0) -1 * n else n
      val denom = d.abs
    
      override def toString = numer + " / " + denom
    }
    

    import org.scalatest.prop.TableDrivenPropertyChecks._
    
    val fractions =
      Table(
        ("n", "d"),
        (  1,   2),
        ( -1,   2),
        (  1,  -2),
        ( -1,  -2),
        (  3,   1),
        ( -3,   1),
        ( -3,   0),
        (  3,  -1),
        (  3,  Integer.MIN_VALUE),
        (Integer.MIN_VALUE, 3),
        ( -3,  -1)
      )
    

    Imagine you wanted to check a property against this class with data that includes some value that are rejected by the constructor, such as a denominator of zero, which should result in an IllegalArgumentException. You could use whenever to discard any rows in the fraction that represent illegal arguments, like this:

    import org.scalatest.matchers.ShouldMatchers._
    
    forAll (fractions) { (n: Int, d: Int) =>
    
      whenever (d != 0 && d != Integer.MIN_VALUE
          && n != Integer.MIN_VALUE) {
    
        val f = new Fraction(n, d)
    
        if (n < 0 && d < 0 || n > 0 && d > 0)
          f.numer should be > 0
        else if (n != 0)
          f.numer should be < 0
        else
          f.numer should be === 0
    
        f.denom should be > 0
      }
    }
    

    In this example, rows 6, 8, and 9 have values that would cause a false to be passed to whenever. (For example, in row 6, d is 0, which means d != 0 will be false.) For those rows, whenever will throw DiscardedEvaluationException, which will cause the forAll method to discard that row.

    condition

    the boolean condition that determines whether whenever will evaluate the fun function (condition is true) or throws DiscardedEvaluationException (condition is false)

    fun

    the function to evaluate if the specified condition is true

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