You may know that the recent Visual Studio Update 2 re-introduces test list functionality in Test Explorer. Traits can be added to coded unit tests by adding a string to the code. Both traits and the Test Explorer playlists require a Test Studio test to first appear in the Test Explorer. If a test does not appear once you open the project containing that test, you may need to restart Visual Studio 2012. Please let me know if this resolves your issue.
All the best,
the Telerik team