I'm unsure how to add tests for this given it requires an app to be installed via MSIX to get a package ID in Windows otherwise `IPackageStatics::get_Current()` returns `0x80073d54`.
I managed to get some tests running in a WinRT application context without too much trouble, I think it would be better to run the tests with it if we intend to check how it is supposed to work.
I'd suggest to split the IDL changes to a separate MR in the meantime, and I'll work on getting some framework available upstream to run the tests.