> If you have a good set of unit tests that test all observable behaviors of a system means you can optimize the logic inside and constantly rerun those tests t

> If you have a good set of unit tests that test all observable behaviors of a system means you can optimize the logic inside and constantly rerun those tests to make sure it's not broken This is a naïve utopian world view. The word "good" is doing all the heavy lifting for you. In the last 15 years I haven't seen a single company that had "good" unit tests. I'm inclined to believe they don't exist. Some of the tests I saw turned out to be good. Most of them weren't. The reality is that if you're committing to unit tests, a big chunk of your tests will be shit. And when that's the case, accelerated optimization is far from guaranteed.