public void TestAccessTokenCredential()
        {
            Config config = new Config
            {
                RefreshToken = "refreshToken",
                DomainId     = "domainId",
                ClientId     = "clientId",
                ClientSecret = "clientSecret",
                ExpireTime   = "2019-10-01T00:00:00"
            };
            Credential accessTokenCredential = new Credential(config);

            Assert.Equal("2019-10-01T00:00:00", accessTokenCredential.GetExpireTime());
            Assert.Throws <AggregateException>(() => { string accessToken = accessTokenCredential.GetAccessToken(); });

            accessTokenCredential.SetAccessToken("accessToken");
            Assert.Throws <AggregateException>(() => { string accessToken = accessTokenCredential.GetAccessToken(); });

            string dateFuture = DateTime.Now.AddDays(1).ToString("yyyy-MM-dd HH:mm:ss");

            accessTokenCredential.SetExpireTime(dateFuture);
            Assert.Equal("accessToken", accessTokenCredential.GetAccessToken());

            accessTokenCredential.SetRefreshToken("test");
            Assert.Equal("test", accessTokenCredential.GetRefreshToken());
        }