This issue is experienced while opening the test explorer or running all tests in VS. To resolve the issue try the following steps:
- Close all instances of Visual Studio.
- Delete all files in AppData\Local\Microsoft\VisualStudio\12.0\ComponentModelCache (Note that directory is located in Local.)
- Restart, if that doesn’t work then start over with step 4.
- From a Visual Studio Command Line do this operation: devenv /setup
The points 1 and 2 should fix the issue. But I found that sometimes more steps are required.