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

Question

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.

This answer seems pretty basic but wasn't completely obvious to me at first. If you (re)build the solution it only builds the projects that are configured to build in the Build -> Configuration Manager

This was my issue, I must have inadvertently changed a build configuration settings or something that caused my test projects not to build (when they previously were). So the Test Explorer window was looking at dlls that were out of date. It became clear to me this was the case after doing a Clean and seeing most of my tests disappear and not come back after a rebuild...further inspection of bin folder showed that these projects weren't being built at all.

I had a working setup (for NUnit2 and NUnit3 depending on the solution, and multiple versions of Visual Studio between 2012 and 2017), and it suddenly stopped working one day: no tests detected in any solution or version of VS.

In my case, it helped to delete %localappdata%\Temp\VisualStudioTestExplorerExtensions. After a restart of VS, everything worked as before.