Build An AAA Test For A Discount Rule
Write a readable AAA unit test for one business rule using minimal setup and one Act.
Expired coupons should not reduce a cart total. The current test goes through checkout UI and fails for unrelated selector changes. Arrange only the required state, Act once, Assert the behavior result. The common trap is proving the expired-coupon rule through a full checkout journey. That adds login, rendering, routing, and selector failure modes to a pure pricing rule. Arrange Create a cart with subtotal 100.00 and an expired coupon for 20 percent off. The setup contains the minimum state that makes the rule meaningful: a price and a coupon that should be rejected. Act Call priceCart(cart, coupon) once and…
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