Dennis Stone, a tester on Team Test, has posted a great walkthrough of using the new test impact feature of 2010.  If you aren't familiar with test impact, it's a feature that tells you which tests execute the code you've changed in a checkin.  Rather than run all of the tests, you can run only the tests that test the code you changed.

Test Impact Walk-through

One of the key areas of focus for Visual Studio Team System 2010 is to enhance the experience for testers. There’s already lots of overview information on many of the new features out there so I’m going to dive right in to one of my favorite new features.

In short, the Test Impact Analysis feature gives you a list of recommended tests based on the changes that were made in a build. As you run your tests through Microsoft Test and Lab Manager (code named Camano) you will have the option to run the Test Impact Data Collector which is one of the many built-in Data Collectors available while running tests. This particular data collector will associate the code paths you execute in your application with the test you are running.

When Team Build generates a new build it will analyze what code has been changed since the last build was done and then provide you with a list of the impacted tests. These are the tests that touch the same pieces of code that were changed since the last build.

For a more thorough explanation of the Test Impact Data Collector read this blog post by Amit Chatterjee.

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Also covering test impact but from a different angle, Jakob Ehn shows how to use and view the results in Visual Studio Team System 2010.