I’m working on a solution containing default Unity project (Assembly-CSharp).
I added a test project to the solution with a reference to Assembly-CSharp. According to IntelliSense, the test project does see the types from Assembly-CSharp, however when I’m trying to build the solution, I’m getting the following error:
Metadata file 'MyProjectFolder\Temp\bin\Debug\Assembly-CSharp.dll' could not be found.
Thus, I'm not able to run unit tests on my Unity project.
Indeed, when I’m building the Unity projects, the .\Temp\bin\Debug folder remains empty even though the build is recognized as successful by VS.
The problem is caused by Disable the full build of projects setting which is new in Unity Tools extension. It prevents the binaries to be created, which speeds up situations when they're not actually being used, like when starting the debugger.

./Temp/bin/Debug folder and I can run unit tests.I made a feature request to VS to make it possible to define this setting at solution level, so that you can have 1 solution for speed and 1 for unit testing. I hope it will get enough votes up: https://developercommunity.visualstudio.com/idea/798543/make-it-possible-to-manipulate-the-disable-the-ful.html
I have the same problem, and regenerate project files did the trick.
Edit => Preferences => External Tools => Regenerate Project Files
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