How do you test a Gmail agent before production?
Use a dedicated Gmail test account or a Google Workspace test domain, then test what breaks at volume: threading, labels, sending quotas, and rate limits. Sending one email always works. Staying inside quota and threading correctly across a real conversation is the hard part.
Start with the official test environment
Use a throwaway Gmail account or a test Workspace domain, and authorize your app with the real OAuth scopes from the Gmail API docs. Never test send flows against a mailbox that belongs to a real person.
Where agents actually break
The happy path is the easy part. An agent that can do the simple version of the task will still fall over on the cases below, and these are the ones worth building tests around:
- A reply that starts a new thread instead of continuing the existing one
- A daily sending quota the agent blows through during a batch
- A label the agent applies that does not exist or is misspelled
- Rate limits that delay or reject rapid sends
- An attachment size or format the API rejects
How to test it properly
Give the agent a realistic starting state, let it run the full task end to end, then check the state it left behind rather than the response it returned. Run the same scenario twice to confirm it does not duplicate work or corrupt state on a retry. Then deliberately inject a failure partway through, a rejected write or a rate limit, and confirm the agent recovers instead of charging ahead as if nothing happened.