[crcarlson]

In addition to essentially input-output test driven development at the unit, subsystem and system levels, I am a huge fan of "design by contract" for identifying both design and implementation errors. In my personal experience no test suite has been fully comprehensive and rigorously placed assertions, invariants, etc. pick up all kinds of design and implementation flaws. I find they also help for debugging by taking the guesswork out of many intermediate possibilities.