How to wait for an event to be triggered in silverlight test

I have a ViewModel that starts loading the Model async in the constructor, and triggers an event when the Model is loaded. I got a test working with the silverlight unit test framework, like this :

bool done = false;

[TestMethod]
[Asynchronous]
public void Test_NoCustomerSelected()
{
    ProjectListViewModel viewModel = null;
    EnqueueCallback(() => viewModel = new ProjectListViewModel());
    EnqueueCallback(() => viewModel.ModelLoaded += new EventHandler<EventArgs>(viewModel_ModelLoaded));

    EnqueueConditional(() => done);
    EnqueueCallback(() => Assert.IsNotNull(viewModel.FilteredProjectList));
    EnqueueCallback(() => Assert.AreEqual(4, viewModel.FilteredProjectList.Count));

    EnqueueTestComplete();
}

void viewModel_ModelLoaded(object sender, EventArgs e)
{
    done = true;
}

But I'm beginning playing with Rx Framework, and trying to get my test to work, but so far I have no luck. Here's 2 attempts :

public void Test_NoCustomerSelected2()
{
    ProjectListViewModel viewModel = null;
    viewModel = new ProjectListViewModel(eventAggregatorMock.Object, moduleManagerMock.Object);

    IObservable<IEvent<EventArgs>> eventAsObservable = Observable.FromEvent<EventArgs>(
        ev => viewModel.ModelLoaded += ev,
        ev => viewModel.ModelLoaded -= ev);

    eventAsObservable.Subscribe(args => viewModel_ModelLoaded(args.Sender, args.EventArgs));
    eventAsObservable.First();

    Assert.IsNotNull(viewModel.Model);
    Assert.AreEqual(4, viewModel.Model.Count);
}

[TestMethod]
public void Test_NoCustomerSelected3()
{
    ProjectListViewModel viewModel = null;

    var o = Observable.Start(() => viewModel = new ProjectListViewModel(eventAggregatorMock.Object, moduleManagerMock.Object));

    IObservable<IEvent<EventArgs>> eventAsObservable = Observable.FromEvent<EventArgs>(
        ev => viewModel.ModelLoaded += ev,
        ev => viewModel.ModelLoaded -= ev);

    o.TakeUntil(eventAsObservable)
          .First();

    Assert.IsNotNull(viewModel.Model);
    Assert.AreEqual(4, viewModel.Model.Count);
}

The first test goes in waiting forever, the second doesn't work because the viewModel is null when it does the FromEvent.

Anyone has a clue on how to do this properly?

Update: Here's a working solution with the help from PL :

[TestMethod]
public void Test_NoCustomerSelected4()
{
    var viewModel = new ProjectListViewModel(eventAggregatorMock.Object, moduleManagerMock.Object); 

    Observable 
       .FromEvent<EventArgs>(viewModel, "ModelLoaded")) 
       .Take(1) 
       .Subscribe(e =>  
           { 
               Assert.IsNotNull(viewModel.Model); 
               A开发者_运维百科ssert.AreEqual(4, viewModel.Model.Count); 
           }); 
}

I believe you still have to use Enqueue calls. E.g. something like this:

var done = false;
var viewModel = new ProjectListViewModel(eventAggregatorMock.Object, moduleManagerMock.Object);

Observable
   .FromEvent<EventArgs>(viewModel, "ModelLoaded"))
   .Take(1)
   .Subscribe(viewModel => 
       {
           Assert.IsNotNull(viewModel.Model);
           Assert.AreEqual(4, viewModel.Model.Count);
           done = true;
       });

EnqueueConditional(() => done);
EnqueueTestComplete();