It's a problem with your code, it doesn't work with chars that aren't in the alphabet. Try in your own IDE with sentences, not single words, for "hello world" your code returns weddk world. Not a kata issue.

"I don't know whether there is an issue with this Kata or an issue with my code" is exactly opposite of the "ISSUE" flag. Why marking a post with ISSUE if it's not known if there is an issue?

And it's difficult to tell what is the problem with your code if we do not know your code.

• In what language?
• What tests exactly?
• What makes you think that the tests are broken, and not your solution?