Huh? Preemptively testing a subset of my code doesn't prevent me from fixing other bugs, or from writing regression tests. From the tone of your question, you

Huh? Preemptively testing a subset of my code doesn't prevent me from fixing other bugs, or from writing regression tests. From the tone of your question, you'd think that 100% test coverage would fix the remaining 20%, when it clearly doesn't. I mean no disrespect, but this is what I meant when I said that unit-test coverage is a pedantic subject (which, I must again insist, is not meant to imply that you are a pedant). The bugs get fixed, they just don't get discovered/resolved with up-front unit tests alone. It ends up being more effective and more efficient to hunt them down by other means.