As there are still tons and tons of native C++ development going on and you need to test that code just like you do for your C# code. I've been using WinUnit, which was first introduced in a great MSDN Magazine article by Maria Blees, for all my native testing and love it. Where previous attempts at C++ native testing fell far short was that you were forced to write the execution infrastructure for every single project. What WinUnit does differently is that not only makes writing the tests simple, but it also it with a fantastic runner that makes running tests simple enough even a manager could do it. I've always summed up WinUnit as NUnit for C++ developers. Whenever it's easy to write tests, you're more likely to do them and WinUnit makes Test Driven Development for C++ nearly trivial.

Maria has moved the WinUnit project to CodePlex at http://winunit.codeplex.com/ so it can grow and prosper. If you're doing native development, you have to use WinUnit!