Spin up ephemeral test inboxes for email integration tests

Most teams test email by not testing it. The send path gets a mock — expect(transport.send).toHaveBeenCalledWith(...) — and everyone agrees that's "good enough." The receive path gets skipped entirely, because there's no honest way to assert on a real inbox from a test runner. So the one part of your system that talks to the outside world over an unreliable, asynchronous, third-party channel is the part with the least coverage. That's backwards. The reason email is hard to test isn't the sending. It's the asserting . You can fire POST /messages/send all day, but to prove the message actually left, rendered correctly, and arrived with the body you expected, you need a real mailbox you control — one you can read programmatically and throw away when the run finishes. Shared Gmail test accounts almost get you there, but they bring OAuth on the runner, catch-all races between parallel workers, and a 90-day token that expires the night before a release. This post is about a different fixture: a disposable Agent Account created at the start of a CI run and deleted at the end. You mint a real mailbox per run (or per test), point your application at it, send and receive real mail, assert on the actual message body, and tear the whole thing down. No OAuth. No shared inbox. No leftover state. What an Agent Account gives you here An Agent Account is just a Nylas grant with a grant_id . That's the whole trick, and it's worth saying plainly because it's what makes this pattern cheap: an Agent Account works with every grant-scoped endpoint you already know — Messages, Drafts, Threads, Folders, Attachments, Webhooks. There's nothing new to learn on the data plane . If you've ever called GET /v3/grants/{grant_id}/messages , you already know how to read a test inbox. The difference from a normal grant is provisioning. A regular grant needs a real human to complete an OAuth flow. An Agent Account is created with a single API call — no OAuth screen, no refresh token, no human. It's a m