Kata

I'd welcome you to add those.

I remember feeling at the time that random tests would be very difficult to write in a way that actually tests anything; you'd have to generate a lot of functions, along with being able to make sure they compile correctly, which in my mind would be difficult to pull off without them all being roughly the same with some random characters thrown in.

And as for more regular tests, what kinds of things would you add?

Well, I can't come up with them immediately even if you ask me so (I did the kata 3 months ago, which is a long time ago), and 4 tests are really far from enough. I'm afraid you'll have to write more tests that has more coverage yourself.