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

            var client = new InstanceIdClient(factory, MockCredential);

            var result = await client.UnsubscribeFromTopicAsync("test-topic", new List <string> {
                "abc123"
            });

            Assert.Equal(1, result.SuccessCount);
        }