SubViewModelTests.cs

[TestFixture]
public class SubViewModelTests
{
    [Test]
    public void RequestSubNavigate_NavigatesToChildViewModel_PassesInMessageId()
    {
        var parentViewModel = new ParentViewModel();

        parentViewModel.GoToChildViewCommand.Execute();

        Assert.AreEqual(1, Dispatcher.NavigateRequests.Count);
        var request = Dispatcher.NavigateRequests.First();
        Assert.That(request.ViewModelType == typeof(ChildViewModel));
        Assert.That(request.ParameterValues.ContainsKey("messageId"));
    }

    [Test]
    public void RequestSubNavigate_ResultMessageReceived_ParentIsNotifiedAndUnsubscribes()
    {
        var parentViewModel = new ParentViewModel();

        parentViewModel.GoToChildViewCommand.Execute();

        var messageId = Dispatcher.NavigateRequests.First().ParameterValues["messageId"];

        MessengerHub.Publish(new SubNavigationResultMessage<string>(this, messageId, "Result 1"));

        Assert.AreEqual("Result 1", parentViewModel.LastResult);

        MessengerHub.Publish(new SubNavigationResultMessage<string>(this, messageId, "Result 2"));

        Assert.AreEqual("Result 1", parentViewModel.LastResult);
    }

    [Test]
    public void ChildView_ReturnsResult_ParentIsNotifiedAndUnsubscribes()
    {
        var parentViewModel = new ParentViewModel();

        parentViewModel.GoToChildViewCommand.Execute();

        var messageId = Dispatcher.NavigateRequests.First().ParameterValues["messageId"];
        var childViewModel = new ChildViewModel(messageId);
        childViewModel.ReturnResult("Result 1");

        Assert.AreEqual("Result 1", parentViewModel.LastResult);

        var secondChildViewModel = new ChildViewModel(messageId);
        secondChildViewModel.ReturnResult("Result 2");

        Assert.AreEqual("Result 1", parentViewModel.LastResult);
    }

    public class ParentViewModel : ViewModelBase
    {
        public string LastResult { get; private set; }

        public IMvxCommand GoToChildViewCommand
        {
            get { return new MvxRelayCommand(() => RequestSubNavigate<ChildViewModel, string>(null, onResult)); }
        }

        private void onResult(string result)
        {
            LastResult = result;
        }
    }

    public class ChildViewModel : SubViewModelBase<string>
    {
        public ChildViewModel(string messageId)
            : base(messageId)
        {
        }

        public new void ReturnResult(string result)
        {
            base.ReturnResult(result);
        }

        public new void Cancel()
        {
            base.Cancel();
        }
    }
}