ITYM "I rarely have bugs in my tests that I'm aware of". The amount of tests I've seen that look like they are working properly, have been "verified" and are buggy is huge. Usually we find they were buggy because someone moves some other tests around or changes functionality that should have broken the tests, but didn't.

Please, don't ever assume that your tests are beyond reproach just because you verified them. Tests are software as well and are as prone to bugs as anything.