Hum can I see the random test code

You can print the input to the console if that's what you mean.

I can't get any output and check what went wrong because of the limited buffer

You should get logs from many tests before you run out of buffer space. Unless you are storing all the names somewhere (emulating the queue) and printing it out at some point - such algorithm will not work at all, and if you're using it, drop the idea and think how you can solve this task by using math.

It's already there:
Your task is to return the first longest string consisting of k consecutive strings taken in the array.