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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- Whenever.scala
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def
whenever[T](condition: Boolean)(fun: ⇒ T)(implicit wa: WheneverAsserting[T]): Result
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 followingFraction
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 usewhenever
to discard any rows in thefraction
that represent illegal arguments, like this:import org.scalatest.matchers.Matchers._ 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 === (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 meansd
!=
0
will be false.) For those rows,whenever
will throwDiscardedEvaluationException
, which will cause theforAll
method to discard that row.- condition
the boolean condition that determines whether
whenever
will evaluate thefun
function (condition
is true) or throwsDiscardedEvaluationException
(condition
is false)- fun
the function to evaluate if the specified
condition
is true