Create Test

Start with the user need or business rule that must always hold, not files, coverage, or internal calls. Inspect for facts; ask only for business decisions that cannot be discovered.

Define the regression contract

Establish:

• actors, goals, and externally observable outcomes;
• business rules and invariants that must never change;
• critical paths and relevant rejection, timeout, retry, permission, concurrency, and partial-failure cases;
• the current baseline and every intended behavior change;
• KPIs with window, data set, acceptable variance, and justified pass/fail threshold;
• systems crossed, production-like data needs, and evidence the available environment can actually provide.

Never invent a metric or threshold; record the gap.

Choose the proof

Prefer the highest reliable boundary:

1. black-box tests through the public API, UI, job, event, or CLI;
2. deep integration with the real database, queue, connector, or protocol;
3. contract, replay, property, or characterization tests for narrower risks;
4. unit tests for isolated rules where a wider test adds no confidence.

Mock only beyond the verified boundary. For database or migration work, read integration patterns. When proving a process manager, worker, container entrypoint, or deployed artifact, exercise the real container or OS image, not only a host process, and verify worker replacement, signal handling, and graceful shutdown where those boundaries apply.

For strategy or audit only, return the contract, prioritized scenarios, proof method, and blind spots. Judge tests by failures caught, not assertion or coverage counts.

Implement when asked

Follow project layout and the development loop. Add the smallest important proof, observe it fail, make approved source changes, then observe it pass.

Assert outcomes, state, events, metrics, and error contracts rather than calls. Run focused and relevant suites. Report what the evidence proves and what it does not cover.