I got that a few times. I think this happens if your code causes the output text to contain any special characters, like {} <> etc. Can't have anyone accidentally or intentionally injecting JS into the site and all. It worked fine once I fixed the code.

Cool, I didn't know about partition

True, also won't work if somebody gave the hash a non-falsey default value

This kata seems to be hopelessly broken right now. Calling Bag.new.count gives NoMethodException, and Bag.new(1,2) gives an exception saying that the ctor wants 0 args, all before anything is even added to the code.

Does anybody know what unit test framework this is using?