It's also good form to specify the exports of modules.

It doesn't really matter here, but it's a good habit to get into.

ETA: imports too, BTW. Not necessarily for Test.Hspec and Test.QuickCheck, but for the user solution module. Prevents things from breaking if user defines a helper function you also define in testing. ( Doesn't catch everything, but makes it a bit more resilient. )

It's good form to have an initial solution that compiles.

Just add pofi = undefined.

You can take the unused import of Test.QuickCheck out of the example tests as well.

I rejected it to absolutely prevent it from being accidentally approved. I think you can fork it and publish the fork.

thank you! that's a good catch. do I have to publish again? or just saving it is enough?

There should not be a reference solution in Example tests.