Cases — Discount Code v1

Executable test cases mapped to MAE scenarios. Each case includes preconditions, steps, expected, and signals/evidence to attach.

See also:

• Brief → ./brief.md
• Design Notes → ./design-notes.md
• Scenarios (MAE) → ./scenarios.md

How to run (quick)

1. Prepare Cart A ($100.00, all eligible) and Cart B ($3.00).
2. Have fixture codes: SAVE15, LESS500, SHIPFREE, NEWUSR.
3. Set headers: Authorization, Idempotency-Key, X-Correlation-Id.
4. Capture artifacts: HAR, JSON, screenshots, logs, traces, metrics.

Case registry (short)

Keep prose out of tables; details below.

Case details

API-Apply-Valid-001 — Apply SAVE15 (percent)

Pre: Cart A exists, user U1, headers set. Steps

1. POST /v1/checkout/{cart}/discounts/apply body { "code": "SAVE15" } + Idempotency-Key: idem:valid1
2. Record response JSON, headers, timing.
3. Fetch /v1/checkout/{cart} to confirm snapshot. Expected

• 200 with applied_code.code = "SAVE15"; discount equals 15% (half-even).
• Totals recomputed; currency correct.
• Header Idempotency-Status absent. Signals/Evidence
• Logs: MSG.discount.apply.succeeded.
• Metric: discount_attempts_total{result="applied"} increments.
• Trace spans: promo.validate, pricing.compute.
• Artifacts: HAR, JSON, trace link, screenshot.

UI-Apply-Valid-001 — UI apply flow

Pre: Web desktop, Cart A loaded, en. Steps

1. Enter SAVE15, click Apply.
2. Wait for totals update. Expected

• New total shows; “Discount applied” toast/message.
• Focus returns to input; screen reader announces update. Signals/Evidence
• Screenshot (light/dark), SR short video, HAR.

API-Remove-001 — Remove code

Pre: Cart A has SAVE15 applied. Steps

1. DELETE /v1/checkout/{cart}/discounts/apply.
2. GET cart. Expected

• 200; applied_code absent; totals revert. Signals/Evidence
• Log MSG.discount.removed; event discount.removed.
• HAR pair; before/after JSON.

UI-Remove-001 — UI remove flow

Pre: UI shows SAVE15 applied. Steps

1. Click Remove.
2. Confirm totals revert. Expected

• Return to original price; focus safe. Evidence: screenshot/gif.

API-Persist-001 — Refresh + login

Pre: Guest U1 applied SAVE15. Steps

1. Refresh page; GET cart.
2. Login; link cart; GET cart. Expected

• Applied code persists; no duplicate events. Evidence: JSON before/after; event counts.

API-Order-Redemption-001 — Place order

Pre: Cart A with SAVE15; payment succeeds. Steps

1. POST /v1/orders (create from cart).
2. Query redemption endpoint/admin. Expected

• discount_redemptions row created; unique redemption_id. Evidence: readback JSON/screenshot; log MSG.redemption.created.

API-FixedCap-001 — Fixed amount capped

Pre: Cart B $3.00. Steps: Apply LESS500. Expected

• Discount = $3.00; total not below zero; rounding to minor units. Evidence: response JSON; note of rounding.

UI-FreeShip-001 — Free shipping eligibility

Pre: Cart A, standard eligible, express not. Steps

1. Apply SHIPFREE.
2. Switch to express; then back to standard. Expected

• standard cost 0; express shows fee again. Evidence: two JSON snapshots; UI video.

API-Reprice-MinDrop-001 — Eligibility lost on change

Pre: Cart A with SAVE15. Steps

1. Remove item to drop below min subtotal.
2. GET cart. Expected

• Code removed or ignored; message available. Evidence: JSON before/after; log ERR.BUSINESS.code.ineligible.

API-Idem-Reapply-001 — Re-apply with same key

Pre: None. Steps

1. Send two identical apply requests with Idempotency-Key: idem:re1. Expected

• First 200; second 200 + header Idempotency-Status: replayed. Evidence: both responses; event counts unchanged.

API-Race-TwoTabs-001 — Race with different keys

Pre: Two concurrent clients. Steps

1. Send two apply requests simultaneously with different keys. Expected

• Single applied state; stable total; no dup events. Evidence: timing logs; final cart JSON.

API-PerUserLimit-001 — Per-user limit

Pre: Code NEWUSR limit 1. Steps

1. Apply on Cart A → expect success.
2. Apply on new Cart C same user → expect failure. Expected

• Second 400 with ERR.BUSINESS.code.ineligible. Evidence: error JSON; metrics show ineligible result.

API-CurrencyMismatch-001 — Fixed code currency mismatch

Pre: Order currency EUR. Steps: Apply LESS500 (USD). Expected

• 400 in v1; taxonomy code for ineligible. Evidence: error JSON; log snippet.

ADM-Override-001 — Agent override

Pre: Admin access; ticket id available. Steps

1. Set override flag; apply code.
2. Read audit log. Expected

• Discount applied; audit shows agent id + reason. Evidence: admin screenshot; audit log JSON.

API-BadFormat-001 — Invalid code format

Steps: Apply @@bad!!. Expected

• 400 ERR.VALIDATION.code.format; no state change. Evidence: error JSON; UI screenshot (optional).

API-Expired-001 — Not started/Expired window

Steps: Apply fixture outside valid window. Expected

• 400 ERR.BUSINESS.code.ineligible. Evidence: error JSON; logs apply.failed.

API-RateLimit-001 — Brute-force attempt

Steps

1. Send 10 invalid codes in 60 s. Expected

• 429 on later requests; Retry-After present. Evidence: limiter metrics; error JSON.

CHA-PromoBrownout-001 — Promo dependency brownout

Pre: Chaos tool ready. Steps

1. Inject 5xx + latency on promo RPC.
2. Apply valid code. Expected

• Breaker opens; UI banner; checkout allowed without discount. Evidence: breaker metrics; synthetic journey remains green.

CHA-TaxTimeout-001 — Tax timeout

Steps

1. Inject timeout on tax RPC.
2. Apply valid code. Expected

• Estimated tax used; order marked for recompute. Evidence: trace with timeout; job log for recompute.

API-Idem-Conflict-001 — Idempotency conflict

Steps

1. Apply with Idempotency-Key: idem:x and { code: "SAVE15" }.
2. Reuse same key with { code: "LESS500" }. Expected

• 409 ERR.CONFLICT.idempotency; original response preserved. Evidence: both responses; idempotency store proof.

UI-Offline-001 — Offline / captive portal

Pre: Throttle network. Steps

1. Go offline; hit Apply.
2. Reconnect; hit Retry. Expected

• Non-blocking banner; state preserved; retry succeeds. Evidence: devtools recording; screenshot.

Negative & edges (add as needed)

• Unicode normalization on codes; whitespace trim.
• Large carts; many lines; performance budgets.
• Multi-tenant isolation; can’t apply other tenant’s private codes.
• Retry after 429 honors backoff; no burst on recovery.

Artifacts to attach

• HAR for apply/remove.
• Response JSONs.
• Screenshots (light/dark, LTR/RTL).
• Log snippets (msgid, err.code, correlation_id).
• Trace links (p99 exemplar).
• Metrics screenshots (latency p95/p99; attempts result).
• CSV result register.

CSV template

case_id,scenario_id,status,owner,evidence
API-Apply-Valid-001,CD-MAIN-001,pass,QA,link://traces/abc
UI-Remove-001,CD-MAIN-002,pass,QA,link://har/remove