.NET Core unit test for testing middleware using TestHost package

TestStartup.cs

using System;
using System.Threading.Tasks;

using Microsoft.AspNetCore.TestHost;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;

using FirstWebApp;

namespace FirstWebApp.Tests
{
    public class Setup 
    {
        public const string ExpectedOutput = "Request handed over to next request delegate";

        public static async Task<TestServer> InitTestServer() 
        {
            var host = await new HostBuilder()
                .ConfigureWebHost(webBuilder =>
                {
                    webBuilder
                        .UseTestServer()
                        .UseStartup<TestStartup>();
                })
                .StartAsync();

            return host.GetTestServer();
        }
    }
    
    public class TestStartup
    {
        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services)
        {
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            app.UseDummyCookieMiddleware();
            app.Run(async context =>
            {
                await context.Response.WriteAsync(Setup.ExpectedOutput);
            });
        }
    }
}