Testing alerting in Google Cloud Monitoring requires a proactive approach, especially with uncommon scenarios. For assertions that almost always pass—such as DNS record verification or health checks—you can simulate failures using synthetic log injection.

The Alerting Signal: assertion_passed: false

At the heart of this strategy is a convention: services perform their internal checks and log a JSON payload with an assertion_passed boolean. When a check fails—be it a DNS mismatch or a stale cache—the service logs {"assertion_passed": false}.