Maybe it would have been simpler to do it a different way in the first place, but I don't really see the need, at this point, to go out of our way to do it _less_ like native, when fixing the tests—which you're not even removing—takes two changed lines.
Making it more straightforward and less broken is the reason for this change. Making it match some implementation details that we for some reason are testing for I don't find productive.
That it doesn't support IAgileObject? I don't know why Mohamad added those, but I'd guess it's either because he some application query for it, or because all of the dxcore documentation appears to be written in WinRT. Both seem quite plausible and both seem good reasons to check something like this.
What else it doesn't support? Other removed lines were checking for unrelated things too. Why would adapter support IDXCoreAdapterList or a factory interface? If application queries something that has no place in implementation, you can verify that of course, but there is no need to have that in tests.