Works fine now.

I had the same problem, was wondering if i got it wrong, entered a similar solution in Python and then it passed. Something seems to be wrong with the Haskell tests.

That's a known problem with preloaded code. That happened shortly after I translated the kata, sorry. However, you can simply remove the import and add normalize, which should be something like

normalize :: Alphabet -> String -> String
normalize (Alphabet (zero:_)) xs = case dropWhile (==zero) xs of
                                     [] -> [zero]
                                     xs -> xs