public async Task SubscribeWithClientFactory() { 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.SubscribeToTopicAsync("test-topic", new List <string> { "test-token" }); Assert.Equal(0, response.FailureCount); Assert.Equal(1, response.SuccessCount); app.Delete(); }