I've installed NUnit Test Adapter for VS2012 + 2013. When I first installed the Adapter tests were showing up, but they stopped showing up for some reason today. After building, rebuilding, cleaning, restarting, nothing shows up in Test Explorer. Why would this be happening? I'm using VS2013 Ultimate.
If you're using a NUnit3+ version, there is a new Test Adapter available.
Go to "Tools -> Extensions and Updates -> Online" and search for "NUnit3 Test Adapter" and then install.