问题:

An exception occurred while invoking executor 'executor://mstestadapter/v2': Constructor on type 'Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.Execution.UnitTestRunner' not found.

回答1:

Exit Visual Studio.
Delete %temp%\VisualStudioTestExplorerExtensions
Restart Visual Studio and try again.
That's all it was.

回答2:

I had the same problem while running tests in the build server.

I tried below things and it started working:

updated my projects to point to latest MSTest.TestAdapter and MSTest.TestFramework
cleared old versions of MSTest.TestAdapter and MSTest.TestFramework folders from build server under this paths

C:\Users\.nuget\packages\MSTest.TestAdapter C:\Users\.nuget\packages\MSTest.TestFramework
I cleared the source files in the build once(not sure about this step but worth trying just in case)