That's a classic! (https://news.ycombinator.com/item?id=46306724) ... but too far from this particular topic to make sense on the list - otherwise we'd probably have to add all SQLite stories, which are legion.

That one's always a good read, particularly the discussion of the tension between 100% coverage testing and defensive programming. We go for maximum defensive programming, so huge numbers of code paths that can't be exercised in testing but that will prevent things running off into the weeds if something does manage to trigger them. Another organisation in contrast had a client who required 100% code coverage in testing so they spent six months removing all the non-testable defensive code in their code base.