Coverage driven testing is (almost) always (mostly) evil. Coverage as a metric is great. Maybe you're not going for 100%, however it does tell you something about your test set(s), providing a decent measure of "doneness". However all of this is depends on good test cases. Test cases that test something. That might sound obvious, but it's fairly easy to achieve 100% coverage while testing nothing. By the way, the reason I said "almost" and "mostly" before, is you can find bugs while attempting to improve coverage; provided you take a step back forget about achieving coverage, and instead write good tests, that happen to get you the coverage. There's a lot of temptation there and it's not an overall good strategy, but you'll find stuff.