What works great for me: I auto test the API of the server/system/library/module I am responsible for. Nothing else. No auto testing of internal details. It l

What works great for me: I auto test the API of the server/system/library/module I am responsible for. Nothing else. No auto testing of internal details. It lets me completely rewrite internals without breaking the tests. The API tests needs to be so good that another developer could implement the same server/system/library/module using the tests only. And the API tests needs to try as hard as possible to break the code being tested. Using this method I have had zero bugs in production for the last 5+ years.