Mine is that the useState hook is an actual plague on the entire React ecosystem. Regardless of your opinions of React, if you wanna use something then use it right.
I've come around to this position after seeing the mess people make.
I just got a new job where I contribute to a fancy open source database. They do have unit tests. Barely. Most things are tested in SQL though. You have to build/link the whole thing to run the tests. But lots of things are plugins so it's fast enough.
If you can get away with it, this is better.