The problem is you're using for...in, read this: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in and in the tests, the array prototype is modified.

You, and the kata's author/translator used a solution var without declaring it (with var or let), that's the problem. I've fixed it in the testing part, I suggest you do that also in your code as good practice.

Can't reproduce it, was it in javascript? Post your code as stated here: https://docs.codewars.com/training/troubleshooting#post-discourse

I have an issue that seems related to the tests and not my code. I get this error if i return the correct string in attempt:

It should work for random tests too - Expected: ['Marge,', 'Barney,', 'Moe,', 'Lisa', '& Ned'], instead got: 'Marge, Barney, Moe, Lisa & Ned'

If I return the array instead of a string, all the random tests pass, but then i fail the basic tests which correctly ask for a string in return, am I missing something or it is just maybe a newly introduced bug with the tests?