NUnit failed to load DLL

I couldn't execute my tests and found that to be one of the issues. It turns out that my TestFixture was internal. Just switching it to public solved my case.

After unsuccessfully trying all other responses above, the following worked for me:

In my case the .NET project and solution is on a mounted drive (I use a MacBook and Parallels for .NET development). The mount also contains the /bin/debug and /bin/release locations where NUnit was attempting to read the "test" DLL from.

The fix was to move the solution/project files to the C: drive of my Windows image. The tests were discovered immediately.

Apparently the shared/mounted location was not to its liking. I don't know why, since the mount is permanent and read/writable to all users on the Windows image. I suspect file permissions problems or maybe somehow the entire mount is not accessible to the user/process running the NUnit discovery logic.

I had a similar issue, the key is the fact that it is the Test Runner in Visual Studio that is stating that only x86 assemblies will be tested. I am assuming from this that it then forces the use of the x86 NUnit runner. To change this (in VS2015 and VS2017 at least), go to Test > Test Settings > Default Processor Architecture > X64.

You can also set the execution target in the runsettings file. You then have to select that file. This should make the solution more stable. A runsettings file which only set this can look like:

To enable it, do as shown in the figure below:

When you select it from the test menu (1), it will be added as the selected one in the menu (2), and a Rebuild will then make the test appear in the Test Explorer (3)

There is an extra bonus by using a runsettings file, and that is that it will then run properly on the TFS Build system, if you use that. I have written a blog post on that issue, see http://hermit.no/how-to-control-the-selection-of-test-runner-in-tfsvsts-making-it-work-with-x86x64-selected-targets/