On Wednesday 25 May 2011 12:40:20, Guy wrote:
I have some functions with preconditions. For example, foo::[a]->IO Bool requires a list of at least three elements, and bar::[a]->Int->IO () requires that its second argument is some position within the list.
How can I test these with quickcheck? If I use ==>, quickcheck gives up with very few test cases.
You could increase the maxDiscard value, ghci> quickCheckWith stdArgs{ maxDiscard = 5000 } (forAll arbitrary (\xs -> (length xs > 2) ==> whatever)) or create a generator that produces only output fulfilling the preconditions: atLeast3 :: Arbitrary a => Gen [a] atLeast3 = do x <- arbitrary y <- arbitrary z <- arbitrary ws <- arbitrary return (x:y:z:ws) ghci> quickCheck (forAll atLeast3 whatever)