Caliburn EventAggregator moq verify PublishOnUIThreadAsync async method

Question

I have an event as following

namespace MyProject
{
    public class MyEvent
    {
        public MyEvent(int favoriteNumber)
        {
            this.FavoriteNumber = favoriteNumber;
        }

        public int FavoriteNumber { get; private set; }
    }
}

And I have a method which raises this event.

using Caliburn.Micro;
//please assume the rest like initializing etc.
namespace MyProject
{
    private IEventAggregator eventAggregator;

    public void Navigate()
    {
        eventAggregator.PublishOnUIThreadAsync(new MyEvent(5));
    }
}

If I using just PublishOnUIThread, the below code (in an unit test) is working fine.

eventAggregatorMock.Verify(item => item.Publish(It.IsAny<MyEvent>(), Execute.OnUIThread), Times.Once);

But how do I check for async version for the same?

eventAggregatorMock.Verify(item => item.Publish(It.IsAny<MyEvent>(), Execute.OnUIThreadAsync), Times.Once);

Facing trouble verifying the async method. Assume private Mock<IEventAggregator> eventAggregatorMock;. The part Execute.OnUIThreadAsync gives error 'Task Execute.OnUIThreadAsync' has the wrong return type.

I also tried

eventAggregatorMock.Verify(item => item.Publish(It.IsAny<MyEvent>(), action => Execute.OnUIThreadAsync(action)), Times.Once);

But says, System.NotSupportedException: Unsupported expression: action => action.OnUIThreadAsync()

Thanks in advance.

Answer 1

IEvenAggregator.Publish is defined as

void Publish(object message, Action<System.Action> marshal);

Therefore you would need to provide a proper expression to match that definition.

eventAggregatorMock.Verify(_ => _.Publish(It.IsAny<MyEvent>(), 
                                It.IsAny<Action<System.Action>>()), Times.Once);

Also PublishOnUIThreadAsync extension method returns a Task

/// <summary>
/// Publishes a message on the UI thread asynchrone.
/// </summary>
/// <param name="eventAggregator">The event aggregator.</param>
/// <param name="message">The message instance.</param>
public static Task PublishOnUIThreadAsync(this IEventAggregator eventAggregator, object message) {
    Task task = null;
    eventAggregator.Publish(message, action => task = action.OnUIThreadAsync());
    return task;
}

so it should be awaited

public async Task Navigate() {
    await eventAggregator.PublishOnUIThreadAsync(new MyEvent(5));
}