I've seen exactly the same problem in VS2012. I have a Unit Test project that works. I add another Unit Test project and none of the tests in that project can be run. The .csproj file is clearly a unit test file, according to the instructions
in http://social.msdn.microsoft.com/Forums/en-US/vststest/thread/2192fac0-0de7-45c6-872a-2be49e95ce2c/ The icon of the new project didn't even include the Unit Test project icon (which is probably a minor bug).
The problem was that the test project didn't include any valid tests. I thought that the test was valid, but they are only valid if they follow a specific signature:
public class SomethingTests
public void testSomething()