Javascript needs random test. Don't know about other language.

Although it doesn't seem to be a problem, you should specify if the test should be case sensitive.

I think it's worth pointing out, that most of our solutions wouldn't work for (1:[2,2..]) as we go in an infinite loop with 1. I think you should either restrict the kata to finite lists or include infinite tests where the repeating character is not the first one. Thinking further there is just no way to terminate for [1..] so then the kata should state that for infinite lists a repeating elem is guaranteed..