500 error when test MVC web API using httpclient and httpserver

i referered this httpclient and httpserver to do integrate test over my MVC API, but get 500 error, i can ensure my action don't have internal error because i can success request during Fiddler. my code is very simple as the referer, i pasted them below. i don't have enough reputation to comment the original question, so asked new question here.

my controller action

[HttpGet]
    [Route("api/InjectDocuments/hello/")]
    public IHttpActionResult Hello()
    {
        return Ok();
    }

my test method

 [TestMethod]
    public async Task InjectDocumentE2ETest()
    {
        var config = new HttpConfiguration();
        //config.MapHttpAttributeRoutes();
        //config.Routes.MapHttpRoute(name: "Default", routeTemplate: "api/{controller}/{action}/{id}", defaults: new { id = RouteParameter.Optional });
        WebApiConfig.Register(config);

        using (var server = new HttpServer(config))
        {

            var client = new HttpClient(server);
            //  client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            string url = "http://localhost/api/InjectDocuments/hello";

            var request = new HttpRequestMessage
            {
                RequestUri = new Uri(url),
                Method = HttpMethod.Get
            };

            request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

            using (var response = await client.SendAsync(request))
            {
                Assert.AreEqual(HttpStatusCode.OK, response.StatusCode);
            }
            using (var response = await client.GetAsync(url))
            {
                Assert.AreEqual(HttpStatusCode.OK, response.StatusCode);
            }
        }
    }