Nice try.

Actually I don't really care if people cheat, but when I saw your solution I just had to create some random tests ;)

I reworked the error messages and now they provide given input, expected output and actual output.

Thank you for your feedback.

I'll look over the testcases and improve them. I don't know if I'll find time for it today, but as soon as they are ready I will let you know it.

First, thanks for the feedback!

You are right, it is a bit misleading, but I didn't think of it because Rot13 was made for the latin/english alphabet. I will change it to make it more clear.