Cover discount and tax rounding at the documented boundary
A 10% promotion on three 19.99 items produces a one-cent difference between the cart and receipt. Add cases that pin down order-level versus line-level rounding.
- Focused work estimate
- 1h 45m + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Boundary testing · Money arithmetic · Contract testing
Estimated field mix
- Quality engineering100%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A small commerce team has happy-path browser tests but still ships rounding and retry defects. Model a fictional shop using synthetic products, a local payment double, and explicit cart rules before adding regression coverage.
Setup prerequisites
- Create or provide a local checkout fixture application.
- Model products, tax rules, inventory, and a payment-provider double using synthetic data.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Tests use the agreed line-discount-then-tax rule and include a half-cent boundary.
- Cart, order, and payment request totals must agree in minor units.
- A discount greater than the eligible subtotal is rejected or capped according to an explicit contract.
Implementation constraints
- Do not reproduce the production rounding helper in expected-value code.
Verification to include
- Assert concrete expected totals for zero, one, and three eligible items.
- Introduce a round-at-order-end defect in the fixture and show the relevant case fails.
Deliverables
- Pricing boundary matrix and regression tests
Rollout and recovery
Gate pricing changes with these deterministic cases; update expectations only with a reviewed rule change.
Value of the work
For the engineer: Practice risk-based test selection, stable browser automation, and diagnosis of intermittent failures.
For the team: Review whether a test suite catches business regressions and explains failures without creating noisy release gates.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.