The best measure for a good enough test suite is subjective: How confident are you that if someone introduces a defect into the code, some test will fail? This isn’t something that can be objectively analyzed, and it doesn’t account for false confidence, but the aim of self-testing code is to get that confidence. If I can refactor my code and be pretty sure that I’ve not introduced a bug because my tests come back green—then I can be happy that I have good enough tests.
