Yeah, probably should be 4 kyu.

You haven't solved a lot of kata's then I reckon

Try this test:

test.assert_equals(solve("aaaZ"),"aaaz")

There is a bug in your code.

This particular case is stated in the description, at the end:

"Not all paths can be made simpler. ..."

The "reducibility" criterion for this kata is a "local" one: you are only allowed to cancel the opposing effects of move N and N+1, if they are opposite, rather than being able to cancel a larger series of moves (like the 4 moves N,S,E,W returning to start).

Or, in the more poetic language of the kata description, ^ this ^ is what the following sentence means:

"Going to one direction and coming back the opposite direction right away is a needless effort."

Not all tests pass, all tests passed until your code threw that error and halted the execution of further tests.

Read this: https://docs.codewars.com/training/troubleshooting