TestServer

Test.cs

private TestServer CreateTestServer() =>
      new TestServer(new WebHostBuilder()
        .UseStartup<FakeStartup>());
        
class FakeStartup
{
  public void Configure(IApplicationBuilder app, IHostingEnvironment env)
  {
    app.Run(async ctx =>
    {
      if (ctx.Request.Path.Value.StartsWith("/expected"))
            await ctx.Response.WriteAsync("Hello World");
      else
        ctx.Response.StatusCode = StatusCodes.Status404NotFound;
    });
  }
}