UNIT-TESTING-BASICS5 MIN READ
Walk Red-Green-Refactor In Small Steps
Apply Red-Green-Refactor to add a small behavior without skipping the failing-test or cleanup step.
Small feature Shipping should be free when the cart subtotal is at least $75. Existing code always returns $5.99. The loop keeps the change small enough to reason about. TDD loop Red -> Green -> Refactor First prove the behavior is missing, then make it pass, then clean the design while the proof stays green. Code first Maybe it works; maybe the test would never catch it Each step has a visible signal. Do not skip the failing-test proof or the cleanup proof. 01 Red 02 Green 03 Refactor 04 Fresh step
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