Practice 04 · State management

Planted bugs (5)

1. The item prices ($89.00, $45.00, $59.00) are static text. If the user changes quantity with the +/− buttons, the line total does not recalculate. The price is hard-coded, not derived from unit_price × qty.
2. The subtotal banner says “2 items” but the cart visibly contains 3 line items (wireless earbuds, laptop stand, USB-C hub). The item count is either wrong or counts unique SKUs rather than total quantity.
3. The subtotal shows $134.00 but this figure is ambiguous: is it the sum of visible line totals, or is it calculated independently? With 1 × $89 + 2 × $45 + 1 × $59 = $238, the displayed $134 does not match either interpretation. The maths is inconsistent.
4. The quantity +/− buttons are plain <button> elements with no onclick handlers and no JavaScript event listeners attached. Clicking them has no effect on quantity, price, or subtotal.
5. The “Proceed to checkout” button is always enabled regardless of cart contents, stock status, or validation state. It should be disabled when the cart is empty or when items are out of stock.

State management testing: verify that every user action (increment, decrement, remove) updates all dependent values (line total, subtotal, item count, tax, shipping) atomically. Static or inconsistent values are red flags.