SignalR UnitTest Hub OnConnected

public class MyHub : Hub
{
    public IMyRepository MyRepository { get; }

    public MyHub(IMyRepository myRepository)
    {
        MyRepository = myRepository;
    }

    public override async Task OnConnectedAsync()
    {
        foreach (var child in MyRepository.GetChildrecn())
        {
            await Groups.AddToGroupAsync(Context.ConnectionId, child.Id.Value);
        }

        await base.OnConnectedAsync();
    }
}

I am stuck - I don't really get how to test such an easy hub. I want to make sure, that the Groups Property of the Hub is set accordingly. However most of the UnitTest projects just set the Groups/Clients as a Mock and the OnConnected is never called.

Anyone got some hints for me?