The language in which I experienced the behaviour one year ago was JavaScript, maybe it was fixed in the meantime.

Please specify the language in which this particular edge case assertion is missing. AFAIK this edge case is tested at least once in JavaScript.

The test cases don't check the case [n > length of the string], but the instructions demand to handle that case:

"If n is greater than the lenght of the string, you should return an array with the only element being the same string."

So currently that part could be left out and you still get to submit your final solution.