public void GivenSomeValidVerifyCredentials_RetrieveUserInformation_ReturnsAnAuthenticatedClient()
            {
                // Arrange.
                var mockRestResponseRetrieveRequestToken = new Mock<IRestResponse>();
                mockRestResponseRetrieveRequestToken.Setup(x => x.StatusCode).Returns(HttpStatusCode.OK);
                mockRestResponseRetrieveRequestToken.Setup(x => x.Content)
                                                    .Returns("oauth_token=aaa&oauth_token_secret=ccc");

                var verifyCredentialsResult = new VerifyCredentialsResult
                {
                    Name = "Some Name",
                    Id = 1234,
                    Lang = "en-au",
                    ScreenName = "Some-Screen-Name"
                };
                var mockRestResponseVerifyCredentials = new Mock<IRestResponse<VerifyCredentialsResult>>();
                mockRestResponseVerifyCredentials.Setup(x => x.Data).Returns(verifyCredentialsResult);
                mockRestResponseVerifyCredentials.Setup(x => x.StatusCode).Returns(HttpStatusCode.OK);

                var mockRestClient = new Mock<IRestClient>();
                mockRestClient
                    .Setup(x => x.Execute(It.IsAny<IRestRequest>()))
                    .Returns(mockRestResponseRetrieveRequestToken.Object);
                mockRestClient
                    .Setup(x => x.Execute<VerifyCredentialsResult>(It.IsAny<IRestRequest>()))
                    .Returns(mockRestResponseVerifyCredentials.Object);

                var twitterProvider = new TwitterProvider(new ProviderParams { Key = "a", Secret = "b" })
                {
                    RestClientFactory = new RestClientFactory(mockRestClient.Object)
                };
                var nameValueCollection = new NameValueCollection
                {
                    {"oauth_token", "aaa"},
                    {"oauth_verifier", "bbb"}
                };

                // Act.
                var result = twitterProvider.AuthenticateClient(new TwitterAuthenticationServiceSettings(), nameValueCollection);

                // Assert.
                Assert.NotNull(result);
                Assert.Equal("twitter", result.ProviderName);
                Assert.NotNull(result.UserInformation);
                Assert.NotNull(result.UserInformation.Id);
                Assert.NotNull(result.UserInformation.Locale);
                Assert.NotNull(result.UserInformation.Name);
                Assert.NotNull(result.UserInformation.UserName);
            }
                GivenExecutingVerifyCredentialsThrowsAnException_AuthenticateClient_ThrowsAnAuthenticationException()
            {
                // Arrange.
                const string exceptionMessage = "some mock exception.";
                var mockRestClient = new Mock<IRestClient>();

                var mockRestResponseRetrieveRequestToken = new Mock<IRestResponse>();
                mockRestResponseRetrieveRequestToken.Setup(x => x.StatusCode).Returns(HttpStatusCode.OK);
                mockRestResponseRetrieveRequestToken.Setup(x => x.Content)
                                                    .Returns("oauth_token=aaa&oauth_token_secret=ccc");

                var verifyCredentialsResult = new VerifyCredentialsResult
                {
                    Name = "Some Name",
                    Id = 1234,
                    Lang = "en-au",
                    ScreenName = "Some-Screen-Name"
                };
                var mockRestResponseVerifyCredentials = new Mock<IRestResponse<VerifyCredentialsResult>>();
                mockRestResponseVerifyCredentials.Setup(x => x.Data).Returns(verifyCredentialsResult);

                mockRestClient
                    .Setup(x => x.Execute(It.IsAny<IRestRequest>()))
                    .Returns(mockRestResponseRetrieveRequestToken.Object);
                mockRestClient
                    .Setup(x => x.Execute<VerifyCredentialsResult>(It.IsAny<IRestRequest>()))
                    .Throws(new Exception(exceptionMessage));

                var twitterProvider = new TwitterProvider(new ProviderParams { Key = "a", Secret = "b" })
                {
                    RestClientFactory = new RestClientFactory(mockRestClient.Object)
                };
                var nameValueCollection = new NameValueCollection
                {
                    {"oauth_token", "aaa"},
                    {"oauth_verifier", "bbb"}
                };
                // Act.
                var result =
                    Assert.Throws<AuthenticationException>(
                        () => twitterProvider.AuthenticateClient(new TwitterAuthenticationServiceSettings(), nameValueCollection));

                // Assert.
                Assert.NotNull(result);
                Assert.Equal("Failed to retrieve VerifyCredentials json data from the Twitter Api.", result.Message);
            }