I have created a unit test project in VS2013, and I\'m using it to create a test suite for my SQL Server 2012 database.
I have created 4 test classes so far and ever
Are you using nUnit? I've just had a similar situation moving to a new pc, causing all existing tests to disappear.
Go to Tools -> Extensions and updates -> Select Online on the left -> enter in the search box top right 'nunit test adapter' and install it.
One rebuild later and the tests appeared again.