Recently while working with xUnit project in my solution the unit tests stopped discovering by the Test Explorer in Visual Studio 2019.
I tried various options like clearling temp folder, updating Visual Studio, restarting Visual studio, clearing .vs folder but none of them worked. The solution which worked for me was to install the following xunit.runner.visualstudio nuget plugin
After installing that package all samey tests started discovering in the test explorer in Visual Studio 2019