On Tue, Oct 6, 2015 at 1:24 PM, Roelof Wobben <
r.wo...@home.nl> wrote:
> Hello,
>
> I have written a function to test if three numbers are the same.
>
> Now I want to test my functions by using quickCheck.
>
> So I thought to test first if all three are the same.
>
> but how can I tell quickcheck that all numbers are the same.
Just have quickcheck generate one number, and use it for all three
arguments, eg:
prop_allSame :: Int -> Bool
prop_allSame x = yourFn x x x
then test the other cases:
prop_different :: Int -> Int -> Int -> Property
prop_different x y z = x /= y && y /= z && x /= z ==> not $ yourFn x y z
That's probably OK for ints, but generally the guard in that style
isn't a great solution, since quickcheck will just keep generating
inputs until the predicate is satisfied. That can take a while, so
you could also manually offset the first input in various ways:
prop_different :: Int -> Int -> Bool
prop_different x y = not $ yourFn x (x + y) (x - (y + 1)) -- I put a
+1 in here to avoid returning true where y = 0,
There are probably other ways to mutate a randomly generated input for
your problem that may work better, but that's the general idea.
--Rogan