ChatHub.cs

using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Microsoft.AspNetCore.SignalR;

namespace ChatHub.IntegrationTests
{
    public class ChatHub : Hub
    {
        public async Task SendMessage(string user, string message)
        {
            await Clients.All.SendAsync("OnReceiveMessage", user, message);
        }

        public Task SendMessageToCaller(string message)
        {
            return Clients.Caller.SendAsync("OnReceiveMessage", message);
        }

        public Task SendMessageToGroups(string message)
        {
            List<string> groups = new List<string>() { "SignalR Users" };
            return Clients.Groups(groups).SendAsync("OnReceiveMessage", message);
        }

        public override async Task OnConnectedAsync()
        {
            await Groups.AddToGroupAsync(Context.ConnectionId, "SignalR Users");
            await base.OnConnectedAsync();
        }

        public override async Task OnDisconnectedAsync(Exception exception)
        {
            await Groups.RemoveFromGroupAsync(Context.ConnectionId, "SignalR Users");
            await base.OnDisconnectedAsync(exception);
        }
    }
}