Testing Observables using NUnit/Moq in MVVM

Mock->setup a function must run for each parameter change.
Obs.Create take in IObser and return IDispoable. So next a Subject to call OnNext.
Note that Subject.sub(Obr) will allow OnNext to stream out Obs.
Finally, testSchedule must advance to see data coming out.

Mock _mockT= Mock;
_VMController = new(_mockT.Object, ...);
[Test] public void IdChanged() {
   Id = new Hashset(){guid};
   _mockT.Setup(p=>ObserveData(Id)
   .Return(GenerateObs(id:Id, data: 100.01));
   Assert.AreEqual(_VMController.ViewModel.DataCollecton.Count,1);
}
IObs<PT> GenerateObs(string id="", double? data=null,DateTime logicalDate=null) {
Data data = new (...);
return Observable.Create(obsr=>{   // Func<IObserver,IDispoable>
var s = new Subject<Data>();
   s.subscribe(obsr);
   onNext<Data>(s,data);
return s;
});
}
void onNext<T> (IObserver obr, T data)
{
  obr.OnNext(data);
  _testSchedule.AdvancedBy(250ms);
}