you need to test by passing something more complex to the function besides ABC. songDecoder("AWUBWUBWUBBWUBWUBWUBC"); This will help you understand why you're getting errors.

That's because without the join, it fails the first test, and with it, it fails the second.

WUB should be replaced by 1 space: expected [ 'A', 'B', 'C' ] to equal 'A B C'           // error message without join
multiples WUB should be replaced by only 1 space: expected 'A  B C' to equal 'A B C'     // with it

The only error is in your code:

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You can try changing Node version to 8 to see all the logs (no matter if your code fails), 10 onwards it stops when it fails one test and the next ones aren't executed.

There is no issue with the kata, your code is wrong.

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And it'll fail with inputs like "AWUBAWUBA" too. Use console.log to evaluate middle values or something like Pythontutor