QA Exercise 3

1. Add 2–3 items with different prices. Try a negative or zero quantity.
2. Apply the coupon SAVE10 multiple times; change quantities after applying it.
3. Remove an item and check which row is deleted; verify subtotals and totals.
4. Compute the expected total yourself (discount once, then tax on the discounted subtotal) and compare.
5. Present your spoken bug report: Title → Steps to Reproduce → Expected vs Actual → Severity/Priority → Recommendation.

• input validation — rules that prevent invalid entries (e.g., negative quantity).
• business rule — product logic that must be enforced (e.g., one-time coupon, tax order).
• subtotal — sum of line totals before discounts and tax.
• rounding — formatting numbers to a fixed precision (e.g., 2 decimals).
• order of operations — sequence for applying discount and tax.
• desync — UI totals not matching internal state due to logic errors.
• off-by-one — using the wrong index when removing/updating items.
• source of truth — the authoritative data structure from which UI is derived.

• enforce quantity limits / reject invalid input
• apply a coupon once / prevent stacking
• calculate tax after discount / round to two decimals
• sync UI totals with state / recompute after changes
• map actions to stable IDs / avoid index-based deletes

• add up — make sense numerically: “The totals don’t add up.”
• boil down to — the core reason is: “It boils down to wrong tax order.”
• back out — undo a change: “We need to back out the coupon stacking.”
• line up — match correctly: “The UI doesn’t line up with the cart state.”
• iron out — resolve: “Let’s iron out rounding inconsistencies.”

Bug title: Coupon stacks repeatedly and tax is calculated before discount; negative quantities allowed; deleting removes the wrong row.

Steps to reproduce: Add “Cable” at $10 ×2 and “Charger” at $20 ×1. Apply SAVE10 twice. Change “Cable” to −1. Remove “Charger.”

Expected result: Coupon applied once (10% off subtotal), negative qty rejected, delete removes the selected row, tax calculated on discounted subtotal with proper rounding.

Actual result: Coupon stacks with each click, negative qty accepted and counted, delete sometimes removes a different row, tax computed on pre-discount subtotal with inconsistent rounding.

Severity / Priority: Major severity, P0/P1 depending on release scope — pricing and tax errors affect billing accuracy.

Recommendation: Enforce qty ≥ 1, lock coupon to single application with idempotent state, compute subtotal → discount → taxable base → tax → total, use stable item IDs for actions, and centralize rounding to two decimals.