Your regression tests sound very similar to what I call perl tests. The perl community was ahead of it's time by distributing a test suite with packages on CPAN

Your regression tests sound very similar to what I call perl tests. The perl community was ahead of it's time by distributing a test suite with packages on CPAN. Tests that come out of bug fixes tend (at least for me) to be complexity tests. Essentially they are a 2x2 test of the interaction of pairs of conditional paths with some interaction between them. This dovetails nicely with Rich's point -- keep things simple but in those few inevitable areas where complexity will arise, make sure you can reason about them. I just write regression tests around them to ensure that my reasoning about them is correct. Rich skips the tests because he's better at remembering or re-reasoning through them again :)