I like having tests but I would bet if you audit you production stack it's very likely that a very large portion of it does not really have tests yet is prob most stable part of your stack like Linux kernel etc.
Of course, just because you haven’t personally written tests for parts of a stack doesn’t mean that you shouldn’t write tests for other parts, especially the parts you’ve created.
Also don’t forget that certain things like Linux are extremely battle-tested. It’s generally unlikely that any piece of software you write will receive that much real-world testing, so a growing set of automated tests will help you cover your own arse.
