Not an issue. Also should be fixed.

Check closely all the places where you're decoding/encoding strings. It could be that you've already encoded that output string back to utf-8 elsewhere, which would explain why string's bytes are not in ascii range. In other words, you might be trying to encode the same string twice.

All of these superfluous encoding/decoding issues could be get rid of if the tests themselves simply declared these strings as unicode in the first place.

It seems fine to me. You could post you code here as a spoiler and I could have a look if you want.