The assertion messages display the inputs clearly, actual and expected results clearly, closing.

Haha lul, did it without RegEx and .length
Still works pretty well tho :D

I made it hard for myself, i filter a[] and b[] for any unique numbers via two sets. (Maybe a new kata?)
Who can read is clearly in the advantage :D
TLDR: Read instructions properly and someone please make the test message less ambigous :)