Comment by nyanpasu64

> Most code doesn't express subtle logic paths. If I test if a million inputs are correctly sorted, I've probably implemented the sorter correctly.

I don't know if this was referring to Zopfli's sorter or sorting in general, but I have heard of a subtle sorting bug in Timsort: https://web.archive.org/web/20150316113638/http://envisage-p...