Is it possible to mock IHubcontext<T> using Moq Framework?

Question

I have a controller which has a IHubContext<T> object injected into the constructor. I would like to unit test adding and removing connectionIds to and from groups. I am asking how I can do this? I tried this:

public interface IMyHubContext :IHubContext<MyHub>
{
    Task AddToGroupAsync(string connectionId, string groupName, CancellationToken cancellationToken = default);

    Task RemoveFromGroupAsync(string connectionId, string groupName, CancellationToken cancellationToken = default);
}

var cs = new CancellationTokenSource();
var ct = cs.Token;


Mock<IMyHubContext> hubMoq = new Mock<IMyHubContext>();
hubMoq.Setup(a => a.RemoveFromGroupAsync("123", $"{groupName}", ct)).Returns(null);

But this generates a compile time error.

Answer 1

The compile time error is generated probably due to passing null to Returns. Since, RemoveFromGroupAsync return type is Task, I think you need to set up this call as below:

hubMoq.Setup(a => a.RemoveFromGroupAsync("123", $"{groupName}", ct))
      .Returns(Task.CompletedTask);