You can either use TestDriven.NET or NUnit and start all dynamic unit tests from the assembly, which is not all that exciting.
OR you can start the much more exciting static unit tests directly from the UnitTests.cs file, just uncomment the line you want to test and press F5 to start the game. Alternatively you can also start unit tests from the command line, e.g. "RacingGameSimple.exe -TestCarModel" will show the car model from the game in a special unit test or "RacingGameSimple.exe -TestRenderTrack" will show the track generation code from, etc.
For more information read the end of Chapter 14 or just take a look into UnitTests.cs