I did the AddRef/Release there because otherwise the bug I am fixing does not actually fix. It will free itself while invoking event handlers and it just causes a lot of issues, and this is also what I think the internal behavior on Windows is from tests I had written earlier.
I don't understand how it makes any difference. Is the application releasing the last reference to the IDeviceWatcher in its event handler Invoke method? If that's really what happens, it'd be good to have the test do the same thing.
Do I need to make more commits for the stubs or can I just leave it for this time?
I think it'd be clearer. And you can indeed change the message to semi-stub with the partial implementation.