This behaviour is by design. Int wraps. ( Int might be 64 bits, but will always be bounded. )

signum and abs is not tested.

But in case you are wondering, the math answer for diff signum should be:

diff signum 0 = undefined
diff signum _ = 0

What is the expected return of

diff signum 0

Indeed, there is a bug in haskell translation:
For very large int, (read x) will give an wrong result: (Int is not a big int, it allows only 2^32 at most)

 (read "12379868686876789689697869868969857344444444444444777777777777777777777777777777777774345945496969" :: Int)
 -8728886484601258615

I think the read function is not important, as it always returns Int

However, the test do not respect the big int. Because I am new to codewars, I am not sure how to contribute to the kata test.