Tricks for repairing Visual Studio if it doesn't work with unit test

Sometimes, Visual Studio doesn't work with unit test. Unit test list can't be loaded when you try to load an old unit test project. Or, it can load the list, but when you try to run the unit test case, Visual Studio just tell you it is not able to run the unit test, blah blah blah...

There must be bugs in Visual Studio or in your unit project settings. Please try the following, the easiest one first:

1. Delete .suo, .vsmdi of your solution then reload your project.
2. Type devenv /setup or devenv /resetuserdata. But please be careful, it will clear your user setting data and Visual Studio will start from a factory state.
3. Check if any references of your unit test project does not work. Just click on the reference, if Visual Studio will bring you to the correct position of the Object Browser, it's the correct reference. Otherwise, not. To fix the reference, first remove the reference, then add it again. If you can't find the reference, probably you have to reinstall the relevant software. The issue I met is TeamSystem.Data.UnitTesting won't work. And the attribute TestMethod is undefined because it is defined in the assembly that hasn't been referenced correctly from the unit test project.