integration-test-designerlisted

A unit suite that mocks the database, the queue, and the HTTP client proves your mocks are configured the way you configured them — it never runs your actual SQL, your migrations, your serialization, or the wiring between layers. That's exactly where bugs slip into production. A full E2E suite catches them but is too slow and flaky to gate merges. This skill designs the layer in between: an integration test that drives a deliberately chosen *slice* of the system through its real boundaries — a real database, a real broker, a real HTTP framework — while stubbing only the genuinely uncontrollable third parties. The deliverable is the chosen seam, an explicit real-vs-stubbed split, an ephemeral-infrastructure plus per-test data-isolation setup, and representative tests that assert on observable outcomes. ## When to use this skill - A bug shipped despite a green unit suite because the suite mocked the very collaborator that broke — a wrong column name, a missing migration, a JSON field that serializes differently than the mock returned. - The wiring or contract *between* layers fails (handler doesn't pass the tenant id to the repo; a queue message round-trips with the wrong shape) and no test exercises the layers together. - The E2E suite is too slow or flaky to run on every PR, so cross-layer regressions are caught late, in staging or prod. - You're standing up a new service and want a fast, real-infrastructure test for the persistence/messaging path before there's anything to