Scenarios (MAE)

Concrete, end‑to‑end scenarios for Discount Code v1. Each scenario uses MAE (Main / Alternative / Exception), has explicit oracles, and lists evidence to attach.

Conventions

IDs: CD-<MAIN|ALT|EXC>-NNN.
Given/When/Then style; short, verifiable steps.
Evidence: HAR, response JSON, screenshots (light/dark, LTR/RTL), logs (msgid), metrics snapshots, trace links.
Use fixtures from the Brief (SAVE15, LESS500, SHIPFREE, NEWUSR).

Test data (fixtures)

Cart A: subtotal $100.00, all items eligible, shipping standard.
Cart B: subtotal $3.00, below min for some codes.
User U1 (first‑time), U2 (repeat).
Locales: en, ar (RTL).
Devices: desktop web (Chrome), mobile web (Safari iOS).

MAIN

CD-MAIN-001 — Apply valid percent code

Given Cart A, user U1 When POST /v1/checkout/c_A/discounts/apply { "code": "SAVE15" } with Idempotency-Key: idem:001 Then

200 with applied_code.code = "SAVE15"
pricing.discount_minor = 15% of eligible subtotal (rounded half‑even)
Logs include MSG.discount.apply.succeeded
Metric increments discount_attempts_total{result="applied"}
Trace shows promo.validate and pricing.compute spans

Evidence: HAR, JSON, metrics screenshot, trace link, UI screenshot showing new total.

CD-MAIN-002 — Remove code

Given Cart A has SAVE15 applied When DELETE /v1/checkout/c_A/discounts/apply Then

200; totals recomputed without discount
Event discount.removed emitted
UI shows prior price; focus returns to input

Evidence: HAR pair (before/after), screenshot, log MSG.discount.removed.

Given Guest user U1 applied SAVE15 on Cart A When refresh page; then login same user (link cart) Then

applied_code persists server‑side; totals consistent
No duplicate apply events; idempotency status not replayed

Evidence: JSON before/after, event log counts, UI screenshots.

CD-MAIN-004 — Place order with discount

Given Cart A with SAVE15 When place order successfully Then

Row in discount_redemptions with unique redemption_id
Event order.created includes discount snapshot
Receipt shows discounted totals

Evidence: DB/admin view screenshot (or API read), receipt PDF/HTML, log MSG.redemption.created.

ALTERNATIVE

CD-ALT-001 — Fixed amount with cap

Given Cart B subtotal $3.00, code LESS500 ($5.00 off) When apply Then

Discount limited to $3.00; total not negative
Rounding to minor units verified

Evidence: JSON totals; rounding note.

CD-ALT-002 — Free shipping on eligible method

Given Cart A, shipping standard (eligible), code SHIPFREE When apply; then switch shipping to express (not eligible) Then

standard cost becomes 0; switching to express restores fee
No item price changes

Evidence: two JSON snapshots; UI switch video/gif.

CD-ALT-003 — Cart changes invalidate eligibility

Given Cart A with SAVE15 applied When remove eligible item so subtotal drops below min Then

Reprice drops discount; message shows “No longer meets requirements”
MSG.discount.apply.failed with ERR.BUSINESS.code.ineligible

Evidence: before/after JSON; log snippet; UI banner screenshot.

CD-ALT-004 — Idempotent re‑apply (same key)

Given Cart A; prepare Idempotency-Key: idem:004 When send same POST .../apply twice concurrently Then

First 200; second 200 with Idempotency-Status: replayed
No duplicate events or double discounts

Evidence: both responses; event counts.

CD-ALT-005 — Two tabs race (different keys)

Given Two browser tabs on Cart A When both apply SAVE15 simultaneously with different keys Then

Single applied state; totals consistent; no duplicate redemptions later

Evidence: timing diagram, logs, final JSON.

CD-ALT-006 — Per‑user limit enforced

Given Code NEWUSR limit 1 per user When U1 applies → succeeds; apply again on new cart Then

Second attempt fails with ERR.BUSINESS.code.ineligible (limit)
Attempts metric shows ineligible

Evidence: JSON, logs, metrics.

CD-ALT-007 — Fixed code currency mismatch

Given Order currency EUR, code LESS500 in USD When apply Then

Rejected (ERR.BUSINESS.code.ineligible) in v1 Evidence: error body; logs.

CD-ALT-008 — Agent override (policy)

Given U1 fails eligibility by small margin; agent applies override in admin When override flag set with reason Then

Discount applied; audit log records agent id + ticket Evidence: admin screenshot; audit log.

EXCEPTION

CD-EXC-001 — Invalid format

When apply code @@bad!! Then

400 ERR.VALIDATION.code.format; input preserved; focus on field

Evidence: error JSON; UI screenshot; SR transcript (optional).

CD-EXC-002 — Not started / expired

When apply SAVE15 outside window Then

400 ERR.BUSINESS.code.ineligible; generic UI copy
No state change to cart

Evidence: error JSON; logs apply.failed.

CD-EXC-003 — Rate limit (brute force)

When 10 invalid codes within 1 minute Then

429 with Retry-After set; limiter metrics increase; no sms/email fired
UI shows “Too many attempts”

Evidence: limiter metrics, error JSON, UI screenshot.

Given promo returns slow 5xx When apply valid code Then

Circuit breaker opens; UI banner “Discount temporarily unavailable”; checkout allowed without discount
Journey SLI remains within budget

Evidence: breaker metrics, logs, synthetic check result.

CD-EXC-005 — Tax service delay

When apply code but tax RPC times out Then

Use estimate; mark order for recompute; user can proceed
Error logged ERR.DEPENDENCY.timeout; retry path available

Evidence: logs, trace showing timeout, follow-up recompute job log.

CD-EXC-006 — Idempotency conflict

When reuse same Idempotency-Key but different payload/cart hash Then

409 ERR.CONFLICT.idempotency; previous response not overwritten

Evidence: both responses, server idempotency store audit.

CD-EXC-007 — Offline / captive portal

When network offline or captive portal during apply Then

UI shows non-blocking banner; local state preserved; retry CTA
No backend event emitted

Evidence: devtools network log, UI screenshot.

Cross‑checks (post‑scenario)

Verify events: discount.applied and discount.removed parity with UI.
Verify metrics breakdown by result: applied | invalid | expired | ineligible | rate_limited.
Verify logs include msgid, err.code, correlation_id.
Verify traces exist for slowest 1% (p99 apply).

CSV seeds (scenario register)

id,type,title
CD-MAIN-001,MAIN,Apply valid percent
CD-MAIN-002,MAIN,Remove code
CD-MAIN-003,MAIN,Persist across refresh/login
CD-MAIN-004,MAIN,Place order with discount
CD-ALT-001,ALT,Fixed amount with cap
CD-ALT-002,ALT,Free shipping eligibility
CD-ALT-003,ALT,Cart changes invalidate eligibility
CD-ALT-004,ALT,Idempotent re-apply
CD-ALT-005,ALT,Two tabs race
CD-ALT-006,ALT,Per-user limit
CD-ALT-007,ALT,Currency mismatch
CD-ALT-008,ALT,Agent override
CD-EXC-001,EXC,Invalid format
CD-EXC-002,EXC,Not started/Expired
CD-EXC-003,EXC,Rate limit
CD-EXC-004,EXC,Promo brownout
CD-EXC-005,EXC,Tax delay
CD-EXC-006,EXC,Idempotency conflict
CD-EXC-007,EXC,Offline/Captive portal

Evidence bundle (attach to PR)

Screenshots: apply/remove success & errors (light/dark, LTR/RTL).
HAR: apply and remove, with timings.
Logs: MSG.discount.apply.*, ERR.* samples.
Metrics: latency p95/p99, attempts breakdown.
Traces: at least one p99 exemplar link.
CSV: scenario run register with status & owners.

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

Scenarios

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