Peli's blog has been on my aggregator for a few weeks now. He is, among other things, responsible for mbUnit, a Generative Unit and Model-based Test Framework. his blog discusses the techniques for the stuff he does plus lots of other goodies.
his latest post discusses implementing “Mutation Testing” in .net, where you “mutate” a tested component at runtime to see if the test actually catches the faults that will occur. For example, changing an “if” clause from true to false and see if the test fails. He does this using RAIL, which is a cool thing on its own that I should play with more.