Unit Testing UWP app that references unmanaged dll causes System.TypeLoadException

Question

Trying to Unit Test a UWP app that has a dependency on a .winmd file. If the unit test calls a method in the app that makes a call on a class in the unmanaged dll then I get a System.TypeLoadException. I've tried referencing different .winmd files and using either MSTest framework or xunit but always get the same error. Other unit tests work fine.

Issue can be reproduced..

• Create a new solution with a Universal Windows test project.
• Add the required nuget packages for xunit(xunit, xunit.runner.visualstudio) or MSTest(MSTest.TestFramework, MSTest.TestAdapter) - it fails with either framework.
• Add a reference to an unmanaged dll. I used SamplesNative.winmd that can be found as part of the Windows UI Dev Labs - https://github.com/Microsoft/WindowsUIDevLabs.
• Create a unit test that calls on the unmanaged dll. Using SamplesNative above I added:
  var helper = new DeviceLostHelper();
• Run unit test and it should fail with - System.TypeLoadException: Requested Windows Runtime type 'SamplesNative.DeviceLostHelper' is not registered. ---> System.Runtime.InteropServices.COMException: Class not registered

Any help would be great. Thanks.

Answer 1

After further testing and help from Microsoft here: https://social.msdn.microsoft.com/Forums/vstudio/en-US/68b9ee55-cd7a-4334-952a-a7ecfff4c6ca/unit-testing-uwp-app-that-references-unmanaged-dll-causes-systemtypeloadexception?forum=vsunittest

I have determined that the issue is relating to Resharper. If I disable Resharper and run the unit tests using MsTest Framework and in Test Explorer than the tests work normally.

I achieved this by un-toggling the Enable MSTest support checkbox in Resharper Options->Tools->Unit Testing->MsTest.