I think you mean `-1` here and `1` below (given the body of the specs).

I also think there might be a nicer way to phrase these examples. Something like "compares the indices of the encodings when the strings have identical non-ASCII-compatible bytes". You could even collapse the two examples into one – we tend to prefer one assertion per example in RubySpec, but since they're testing two sides of the same coin, it doesn't seem too bad.