Fixed.

Don't modify the array of functions.

Haha whoops, did not pay attention. I'll revise my answer at some point in time (@ future me who is reading this: come on, fix it)

There is a bug in the test case where it generates the strings to test. It randomly selects 1 character as "duplicate" and randomly inserts it in the string, but it doesn't guarantee any certain number of times that it will occur... it could occur once or not even at all. So it's possible that none of the characters would be repeated, but still have a ')' character in the expected result. It's fairly unlikely, but possible.

Unfortunately I don't think it can be fixed... test cases can't be edited once it's out of beta and more than 500 people have completed the Kata. If it happens, just re-submit and you'll likely pass as long as there's not another bug in your code somewhere.