NUnit Unit tests not showing in Test Explorer with Test Adapter installed

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.

If your test project is set to target a 64bit platform, the tests won't show up in the NUnit Test Adapter.

My test assembly is 64-bit. From the menu bar at the top of visual studio 2012, I was able to select 'Test' -> 'Test Settings' -> 'Default Processor Architecture' -> 'X64'. After a 'Rebuild Solution' from the 'Build' menu, I was able to see all of my tests in test explorer. Hopefully this helps someone else in the future =D.

Check for NUnit versions mismatch. The currently available NUnit Test Adapter only works for NUnit version 2.6.4 and below. To downgrade NUnit from version 3.x go to Package Manager Console > update-package NUnit -version 2.6.4

http://jeremybytes.blogspot.co.ke/2015/11/review-of-unit-testing-makes-me-faster.html

In my situation the 'NUnit3 Test Adapter' has been disabled. To re-enable it go to menu

Tools->Extensions and Updates...

On the left side select 'Installed'->'All'.

On the upper right corner search for 'nunit'.

If you have 'NUnit3 Test Adapter' installed, with the found item you can enable/disable it.