Haskell:
I keep getting:
should work for random collections and ipp values
✘ Falsifiable (after 1 test):
expected: Nothing
but got: Just 0
[]
Positive {getPositive = 1}
0
and I have no idea why... Anyone had the same problem and could provide some test case? In my opinion it works just the way it should... Is that some kind of a test bug (I've read some comments about problems with random test cases)?

Ok... I really don't get it - when the IntPredicate createFilter produces should return true? I've tried like all possible combinations...

For me the most logical would be: c -> c != filterWhat || keep;