MSTest cannot find TestAdapter.dll

Question

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.

Answer 1

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.

Answer 2

For anyone else who stumbles on this question, the problem was caused because a few of my test projects didn't have the MSTest.TestAdapter NuGet package included. I added the MSTest.TestAdapter package to all of my test projects, and the problem seems to be solved permanently now.

Answer 3

I spent the whole last week trying to solve the same issue. Only yesterday did I realize that running tests from the console is a time saver. Much to my surprise, I've just moved all my project -which was inside a "OneDrive" folder, to a different location. Now, it works like a charm! All my tests run from the Visual Studio IDE. I don't know if moving the files had anything to do with it, but you can give it a try.

Answer 4

Reinstalling all solution's Nuget packages fixed this issue for me.

Please run this command on the package console:

Update-Package -reinstall

then try again, or restart VS, then try again.

Reference: https://ardalis.com/force-nuget-to-reinstall-packages-without-updating/