I like a lot the distinction that I first saw mentioned at Google Is your test actually testing functionality or is merely change detector? For example, unit

I like a lot the distinction that I first saw mentioned at Google Is your test actually testing functionality or is merely change detector? For example, unit test has copy-pasted sql query and breaks if you reformatted it etc? If it's change detector, it should be deleted, because it's just copy/different representation of the same information. This is very clear definition that helps argue and think about tests a lot, especially about mythical numbers like "90% unit test coverage".