void AssertValidRequest(String uri, HttpRequestMessage r, HttpMethod method = null)
 {
     if (method == null)
     {
         method = HttpMethod.Get;
     }
     Assert.AreEqual(r.Method, method);
     Assert.AreEqual(r.RequestUri.ToString(), client.baseUrl + uri);
     Assert.IsNotNull(r.Headers.Authorization);
     Assert.IsNotNull(r.Headers.UserAgent);
     Assert.AreEqual(r.Headers.UserAgent.ToString(), client.GetUserAgent());
     Assert.AreEqual(r.Headers.Accept.ToString(), "application/json");
 }