[Haskell-cafe] quickCheck problem

[Bryan Richter]

On Tue, Oct 06, 2015 at 10:24:03PM +0200, Roelof Wobben 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.

Easy, just generate a single number. :) Make it correct by
construction.

    prop_allSame x =
        yourFunc x x x == True

> and second question :  hwo do the test likeif two numbers are the same.

Now the hard part is not generating two numbers that are the same, but
generating two *different* numbers. To do that you may need to create
a custom generator.

unequalPair = do
    x <- arbitrary
    y <- arbitrary `suchThat` y /= x
    return (x,y)

Now you can use that generator:

prop_twoSame = forAll unequalPair $ \(x,y) ->
    yourFunc x x y == False
    -- But you might want to test all permutations!
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: Digital signature
URL: <http://mail.haskell.org/pipermail/haskell-cafe/attachments/20151007/0ba32941/attachment.sig>