We have been using rspec on my project for the unit testing of our Ruby code and while running one of the specs last week I ended up getting this somewhat en-cryptic error message:

After convincing myself that this error wasn’t actually possible it turned out that I had somehow entered an 'invisible to TextMate' character after one of the method definitions - on the editor it just looked like a space.

I’m not sure exactly what the character was but deleting it got rid of the error and got my test/spec running again.