One of the lesser-known features added to .NET 4.0 is the TestCategory attribute. Comparable to the Category attribute in NUnit –this allows you to group your tests in functional categories. Using test categories is now the preferred way of running groups of tests, and you no longer need to deal with tests lists (.vsmdi files), which are tedious to maintain and very difficult to merge.
You can use these test categories to optimize the build experience when using Team Build 2010. In the Build Definition there is a new option that allows you to include, exclude, combine,… multiple test categories in a build. Read more about it on MSDN.