private 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");
        }