Spring relay integration tests: prove the boundaries H2 cannot

What the local suite proves

ScheduledOutboxPollerTest proves that Spring schedules a callback, the local H2 row is selected and claimed, a fake transport can fail once and retry, a batch cap leaves one row pending, and an already-applied event does not mutate stock twice. OutboxRelayFlowTest separately checks logical due times, parked work and token-fenced acknowledgement. Both suites run in one process.

Those facts do not establish two-worker claim fairness, broker persistence, broker redelivery, target-database isolation, shutdown drain or crash recovery. The scheduler lesson names the first boundary; the cut-point lesson names the duplicate boundary.

Next test matrix

Run two worker instances against the target database. Race claims for the same due row and assert one current token. Add a real transport test: confirm publish, kill the relay before acknowledgement, restart, then assert one business mutation. Inject a lost publish response, slow consumer, permanent payload rejection, expired lease and broker outage. Check row state and metrics after each cut point.

Keep test clocks controllable for exact due-time checks, then add a small number of real scheduling tests. Avoid sleeps as the only evidence. Use a latch or observable state with a deadline so failures are bounded and reproducible. The current scheduled fixture uses a latch; it does not replace a process-kill test.

Checked source

mvn -q -Dtest=ScheduledOutboxPollerTest,OutboxRelayFlowTest test

Verification boundary

ScheduledOutboxPollerTest and OutboxRelayFlowTest run locally. The excerpt is shortened or a labelled design sketch; the source kit contains the complete checked fixture.

Costs and limits

No target database, broker, containerized multi-instance environment, process-kill setup or deployment probe is included in this source kit.

Common Mistakes

• Do not report H2 scheduling as broker delivery.
• Do not infer cross-node claim safety from one scheduler thread.
• Do not use an unbounded wait for an asynchronous assertion.

Read next

Spring TaskScheduler: poll committed outbox rows in the background, Spring scheduled relay: recover when the consumer commits before acknowledgement, Spring relay failure trace: inspect persisted state at each cut point, Spring project: turn the local outbox model into a measured relay.

Continue with lease race checks

Continue with Spring outbox claim race: one conditional UPDATE wins.