'await' works, but calling task.Result hangs/deadlocks

You're running into the standard deadlock situation that I describe on my blog and in an MSDN article: the async method is attempting to schedule its continuation onto a thread that is being blocked by the call to Result.

In this case, your SynchronizationContext is the one used by NUnit to execute async void test methods. I would try using async Task test methods instead.

Acquiring a value via an async method:

var result = Task.Run(() => asyncGetValue()).Result;

Syncronously calling an async method

Task.Run( () => asyncMethod()).Wait();

No deadlock issues will occur due to the use of Task.Run.