Test discovery fails to find any tests, because of deleted temporary files

[kkostrzewa]

NUnit3TestAdapter version 3.9.0
Visual Studio 2015 version 14.0.25431.01 Update 3

It appears that NUnit3TestAdapter uses %temp%\VisualStudioTestExplorerExtensions\NUnit3TestAdapter.3.9.0 to store some test adapter .dlls.

My Windows 10 came preconfigured (Settings / System / Storage / Change how we free up space automatically) to "Delete temporary files that my apps aren't using".

I believe this deleted files under %temp%\VisualStudioTestExplorerExtensions\NUnit3TestAdapter.3.9.0 but not the %temp%\VisualStudioTestExplorerExtensions\NUnit3TestAdapter.3.9.0 directory, which caused test discovery to fail to find any tests.

Deleting the %temp%\VisualStudioTestExplorerExtensions\NUnit3TestAdapter.3.9.0 directory and reloading the .sln causes the temp location to get filled out again, which causes test discovery to work.

[OsirisTerje]

Hi! It is not the adapter that uses that temporary folder, it is the Visual Studio test system that places the adapter dll's there. The issue you mention is known, but perhaps not communicated well enough, and I believe it has been fixed in latest version of Visual Studio (but will do an extra check about that).
I have posted this blogpost earlier about this: http://hermit.no/how-to-resolve-cases-of-visual-studio-no-tests-appearing/ (See Crash Fixes at the bottom there), and is also documented in the #261 issue.
The cure is, as you have found yourself, is to simply delete the cache folder in the temp directory. The IFix tool can also do this for you doing: IFix vstestcache -f .
On my machine it looks now like:

(Update)
I have got it confirmed that this issue was resolved in Visual Studio 2017, Update 15.7