Well yeah, sometimes messages from JUnit can be confusing :( The special characters you see are not a part of the string. That's how JUnit attempts to hint you where your answer differs from the expected one. Expected and actual values are different somewhere in between the brackets.

Hey it was java. I did get an error that expected revesed string like that: "Just gniddik [ereht is llits] one more"

If it was indeed in Java, there are no other characters. If it wasn't, raise another issue, stating which one it was.

When reporting an issue, state the language you're referring to, this kata has many, is it Java?

I think description should be changed. It says "Strings passed in will consist of only letters and spaces." but actually there are other special characters which description doesn't say how to treat.