# Concurrency and idempotency

**Test family:** `CONC`

Apply these to the task, not mechanically to every pixel. Cross-cutting failures often emerge only through interactions with domain item files.

- **CONC-001** Double-click, Enter repeat, client retry, proxy retry, job retry, webhook retry, and support replay produce intended single effect.
- **CONC-002** Two users edit same/different fields and receive explicit merge/conflict/last-write semantics.
- **CONC-003** Update/delete, approve/withdraw, cancel/complete, pay/cancel, assign/disable races converge legally.
- **CONC-004** Unique constraints, counts, quotas, seats, inventory, numbering, and ownership are atomic.
- **CONC-005** Out-of-order events and stale clients cannot roll state backward.

## Comprehensive per-item coverage

- **CONC-006** Apply the quality concern to absent, empty, ordinary, boundary-size, malformed, stale, concurrent, and failure-state data.
- **CONC-007** Include text containing ASCII emoticons, emoji/ZWJ sequences, kaomoji, accents, mixed scripts, RTL, combining marks, confusables, invisible characters, and control characters.
- **CONC-008** Exercise UI, API, import/export, automation, mobile, background jobs, notifications, analytics, logs, caches, and stored representations.
- **CONC-009** Test anonymous, ordinary, privileged, suspended, removed, and cross-tenant actors with least privilege and final-commit authorization.
- **CONC-010** Use fresh, stale, conflicting, deleted, archived, and partially migrated records; expose uncertainty rather than silently choosing.
- **CONC-011** Repeat and race operations before commit, after commit before response, and after partial downstream success; require safe idempotency.
- **CONC-012** Force timeout, disconnect, quota, dependency error, malformed response, regional failover, and recovery failure.
- **CONC-013** Use supported browsers, devices, network qualities, locales, time zones, input methods, and assistive technologies.
- **CONC-014** Measure median and tail latency, throughput, resource use, queue depth, retries, and degradation at normal and supported boundary load.
- **CONC-015** Use inert injection canaries across markup, script, SQL, templates, commands, paths, headers, CSV formulas, and logs.
- **CONC-016** Inspect URL, referrer, DOM, storage, clipboard, telemetry, logs, traces, notifications, exports, caches, backups, and screenshots for leakage.
- **CONC-017** Verify labels, roles, names, descriptions, focus, keyboard behavior, announcements, reflow, contrast, motion, alternatives, and error recovery.
- **CONC-018** Translate and lengthen text, switch RTL/LTR direction, change number/date/currency formats, and use unsupported glyph fallbacks.
- **CONC-019** Delete, restore, archive, expire, retain, export, anonymize, and purge; reconcile user-visible, indexed, cached, and backed-up state.
- **CONC-020** Verify one coherent audit trail with actor, authority, target, old/new state, time, source, correlation ID, attempts, and outcome.
- **CONC-021** Define observable success and failure signals, alert thresholds, dashboards, ownership, runbooks, and a way to test the monitors.
- **CONC-022** Compare intended requirement, implementation, deployed behavior, and evidence; do not promote inspected code or a single run into a pass.
- **CONC-023** Segment results by role, tenant, locale, platform, data shape, load, and consequential workflow so averages do not hide severe failures.
- **CONC-024** Run destructive, high-volume, privacy-invasive, and security probes only in an authorized isolated environment with recovery and stop conditions.
- **CONC-025** State residual risk, untested combinations, evidence tier, confidence limits, rollback trigger, and owner before recommending release.

[Back to Cross-cutting quality index](../../cross-cutting.md)
