Totally agree. And when I'm not sure, I used randomized testing against a trivial but slow implementation to make sure that it also works for all the edge cases

Totally agree. And when I'm not sure, I used randomized testing against a trivial but slow implementation to make sure that it also works for all the edge cases that I didn't think of: https://github.com/openlayers/ol3/pull/418/files#L12R552 https://github.com/openlayers/ol3/pull/418/files#L12R552 Haskell's QuickCheck is two generations ahead here. Not only does QuickCheck check random cases, it's also clever enough to refine those random checks into concrete edge cases.