SignalR callbacks not firing in .NET Core integration Test

I have trying to write integration tests for my SignalR chat application. But the connection.On() callbacks never gets fired. While debugging I have made sure InvokeAsync works perfectly fine but not the callbacks Also I have tested my hub with Angular client and it works fine.

Test.cs

public sealed class ChatHubTest : ControllerTests
{
    private IHost? host_;
    [Test]
    public async Task ReplyWithTheSameMessageWhenInvokeSendMethod()
    {
        //var message = "Integration Testing in Microsoft AspNetCore SignalR";
        string echo = "";

        var hostBuilder = new HostBuilder()
            .ConfigureWebHost(webHost => _ = webHost
                .UseTestServer()
                .UseStartup<Startup>()
                .UseEnvironment("IntegrationTest"));

        host_?.Dispose();

        host_ = await hostBuilder.StartAsync();

        TestServer server = host_.GetTestServer();

        var connection = new HubConnectionBuilder()
            .WithUrl(
                "http://localhost:5000/hub/chat?username=21671", options =>
               {
                   options.AccessTokenProvider = () => Task.FromResult("hello");
                    options.HttpMessageHandlerFactory = _ => server.CreateHandler();
               })
            .Build();

        using IDisposable handler = connection.On<(int, string)>(WebSocketActions.GroupAction, msg =>
        {
            (_, echo) = msg;
            _ = echo.Should().Be("Typing");
        });
        await connection.StartAsync();

        await connection.InvokeAsync("JoinGroup", "group1");

        await connection.InvokeAsync("SendToGroup", "group1", 123, "Typing");


        _ = echo.Should().Be("Typing");
    }
}

Hub.cs

public sealed class ChatHub : Hub
{
    ////////////////////////////////////////////////////////////////////////////////////////////////////
    /// <summary>   Join a socket group </summary>
    ///
    /// <param name="group">   Identifier for the group. </param>
    ///
    /// <returns>  . </returns>
    //[Authorize(Policy = "CustomHubAuthorizatioPolicy")]
    public async Task JoinGroup(string group)
    {
        await Groups.AddToGroupAsync(Context.ConnectionId, group);
    }

    ////////////////////////////////////////////////////////////////////////////////////////////////////
    /// <summary>   Send action to group </summary>
    ///
    /// <param name="group">   Identifier for the group. </param>
    /// <param name="userId">   Identifier for the user. </param>
    /// <param name="action">   Action to send </param>
    ///
    /// <returns>  . </returns>
    //[Authorize(Policy = "CustomHubAuthorizatioPolicy")]
    public async Task SendToGroup(string group, int userId, string action)
    {
        await Clients.Group(group).SendAsync(WebSocketActions.GroupAction, userId, action);
    }

    ////////////////////////////////////////////////////////////////////////////////////////////////////
    /// <summary>   Leave group </summary>
    ///
    /// <param name="group">   Identifier for the group. </param>
    ///
    /// <returns>  . </returns>
    //[Authorize(Policy = "CustomHubAuthorizatioPolicy")]
    public async Task LeaveGroup(string group)
    {
        await Groups.RemoveFromGroupAsync(Context.ConnectionId, group);
    }
}

The hub works with angular client. Thanks In Advance.