There do not appear to be specific tests for solution's handling of capitalisation, something like ("A b","C a") -> ["a"]. Same for allowed and disallowed punctuation, I think.

Also, having running phrases is nice, but for debugging, starting with simpler, artificial inputs is better.

You need lots more tests if you want to reliably discern conforming from non-conforming solutions.

No random tests.

Initial code should compile.

Also, giving inputs and output, if possible with type hints, would be nice.

Something like function solution(string0,string1) { return [ "word" ]; }.