The problem is some stuff is a real pain to test with static assertions. Such as I was saying about compilers. It would be a real pain to maintain an expected AST in a unit test, then you'd have to go rework it all if you change the shape and or add/remove nodes etc.

You can mix the approaches, have some static assertions(as sanity checks) but make most snapshot tests. Like I said I wouldn't use snapshot testing for a fibonacci method, but there are problems out there that are a real pain to test via static assertions.