MSTest cannot find TestAdapter.dll
I'm using the built-in Visual Studio test tools (Test -> Run -> etc in the menu). I just started having a problem where I get the following error when I try to run tests
[3/29/2018 1:39:14 PM Error] System.IO.FileNotFoundException: C:\Users\brubin\AppData\Local\Temp\VisualStudioTestExplorerExtensions\MSTest.TestAdapter.1.1.18/build/_common/Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.dll
at Microsoft.VisualStudio.TestWindow.Controller.TestPlatformProvider.PerformShadowCopy(IEnumerable'1 testExtensions)
That's followed by some errors that say
Make sure that test discoverer & executors are registered and platform & framework version settings are appropriate and try again.
When I look at the folder C:\Users\brubin\AppData\Local\Temp\VisualStudioTestExplorerExtensions\MSTest.TestAdapter.1.1.18/build/_common/, there are no files in that folder. However, I haven't knowingly changed anything about my test setup and this was working several days ago, so I don't know why it would have stopped working.
My projects are using the MSTest.TestFramework (MSTest V2) version v1.2 NuGet package.
One thing I noticed that may have caused this problem is that if I go to Tools -> Extensions and Updates, I see that my Microsoft Visual Studio Test Platform was updated a few days ago, on 3/23 (I think that's when I installed a Visual Studio update). However, if that broke something, I have no idea where to look to see what's broken, or how to fix it.
For me, clearing the VisualStudioTestExplorerExtensions folder and restarting Visual Studio (as per this github issue) did the trick. In my case, it contained two folders for different versions of MSTest.TestAdapter, I don't know whether or not that's relevant.