Microsoft recently announced a new initiative called Dev Labs. It appears to be essentially equivalent in concept to Google Labs. They post projects they've been working on and claim no responsibility for current or future outcomes (ain't life grand when you can just wash your hands of responsibility?).  

Anyway, one of the inaugural projects is called Pex, and it looks like it could be a helpful utility. I haven't had a chance to use it yet, but would like to give it a try. The requirements look undoable at the moment though as I don't know how to get my hands on Visual Studio 2010 Team. Here's a description of the program:

Pex (Program EXploration) produces a traditional unit test suite with high code coverage. A parameterized unit test is simply a method that takes parameters, calls the code under test, and states assertions. Given a parameterized unit test written in a .NET language, Pex automatically produces a small unit test suite with high code and assertion coverage. To do so, Pex performs a systematic white box program analysis.

Pex learns the program behavior by monitoring execution traces, and uses a constraint solver to produce new test cases with different behavior. At Microsoft, this technique has proven highly effective in testing even an extremely well-tested component.