Last month I mentioned a couple upcoming tools for "next generation unit testing", but it should come as no suprise that Microsoft is also working on a similar tool of their own. From the maker of MbUnit, Pex is a unit testing framework that auto-generates test inputs for you. So, if you write a test like this:

[PexTest]public void MyTest(string input){...}

Then Pex is smart enough to generate tests for the full range of values for "input":

MyTest(""); MyTest(null); MyTest("somevalue");

Add in auto-correction, and the result is a pretty impressive test-driven development story. Unfortunately, this is currently only a Microsoft Research project. Hopefully it sees the light of day sometime soon (and not just for Team System!).