If you remember Visual Studio 2010 () there was a nice feature called Test Impact Analysis. It used to analyse your test suite and provide a report of what’s being touched.
In Visual Studio 11 this feature is no more available in the IDE, but it’s inside the Team Build, and enabled by default.
If you go through the Build Definition settings, and you look at the Process Template for the build, you can see the Test Impact Analysis is still there:
And it’s enabled by default