This isn't a case, it is

• list of numbers OR a string

If you haven't solved it yet and still want to:

The test case you are having problems with is probably "YA".
I'm guessing your check for vowels does not include uppercase vowels, and so your program just adds an "ay" to the end, thinking there are no vowels.

the y must go after the "a" because is a consonant and you must add after this "ay" so the solution is "ayay".

In all three languages an empty string is to be returned if the empty string is the input itself, as it containes no character other than [A-Za-z ]; fixed the description to make it more clear :)

In test 10 an empty array is passed in for javascript and an empty object for ruby and python, the return statement should be 'Not a string' for any of those cases

Fixed. Thank you for noticing.

Agreed, method signature doesn't match the calls in the description. And variable names 's' and 'xs' are not descriptive. Bad test.