Good call on testing with the numbers in the description. It would be great if the "Unknown error" could be changed to something else, as bouncing between that and the "It took long than 6000ms" error implies an issue with the site. Nonetheless, thanks for the guidance :)

I don't know if this is an issue with the kata's setup, or if it's the site itself, but my solution keeps failing to execute. All my unit tests are passing, including fib(1000), and they take < 1s. The kata's unit tests, however, aren't even running anymore. They just keep failing with "Unknown error" or "Process was terminated. It took longer than 6000ms to complete".