public async Task UnsubscribeWithClientFactory()
        {
            var handler = new MockMessageHandler()
            {
                Response = @"{""results"":[{}]}",
            };
            var factory = new MockHttpClientFactory(handler);

            var app = FirebaseApp.Create(new AppOptions()
            {
                Credential        = GoogleCredential.FromAccessToken("test-token"),
                HttpClientFactory = factory,
                ProjectId         = "test-project",
            });
            FirebaseMessaging messaging = FirebaseMessaging.GetMessaging(app);

            Assert.NotNull(messaging);
            Assert.Same(messaging, FirebaseMessaging.GetMessaging(app));

            var response = await messaging.UnsubscribeFromTopicAsync("test-topic", new List <string> {
                "test-token"
            });

            Assert.Equal(0, response.FailureCount);
            Assert.Equal(1, response.SuccessCount);
            app.Delete();
        }