Attempt at XUnit unit testing leads to WinRT.ActivationFactory errors

[MarkBrainfire]

I've been using XUnit to develop unit tests for .NET 6 class libraries. Now I want to do unit testing for Windows APP SDK class libraries. Is it even possible to unit test a WinUI 3 class library?

I modified a .NET 6 XUnit project to target net6.0-windows10.0.19041.0. This enables the Test Explorer to run the XUnit test and do simple .NET 6 assertions about native .NET types. However, the moment I try and reference something in Windows App SDK, for example Microsoft.UI.Text.FontWeights, I get WinRT.ActivationFactory errors. How can I overcome this?

[DrusTheAxe]

How is your XUnit test built?

I assume your project is just producing a DLL i.e. it's unpackaged, not [MSIX] packaged.

Is it using the Bootstrapper?

Does your project specify <WindowsAppSDKSelfContained>true</>?