Thanks Emanuel, and sorry for the long delay in getting a review!

My main substantive comment is that the approach of hardcoding the recursion count won't work cross platform, as the default recursion limit is set differently depending on how the platform's C runtime behaves. Fortunately, sys.getrecursionlimit() and len(inspect.stack()) should make it possible to tweak the tests to avoid the hardcoded assumption.

I also have some additional readability suggestions, which can be found in Rietveld.