test-driven-development

Test-driven development reduces uncertainty by ensuring code changes are backed by executable proof rather than assumptions. You establish proof-first quality by turning behavior changes into failing-then-passing executable tests.

To write a failing test for behavior verification, establish a failing-first or baseline-first proof. Confirm the initial test exposes the intended behavior boundary before applying any implementation changes.

To pass failing tests, make the smallest code change needed to turn the failing proof into passing evidence. This minimal implementation approach ensures you satisfy the test chain without over-engineering.

You need executable tests for regression prevention when you want to keep the test chain active so future changes do not silently reintroduce the problem. This creates a regression guard by construction.

Yes, test-driven development works for bug fixes by establishing a concrete verification baseline that exposes the issue. You then apply minimal implementation changes until the passing test evidence serves as the acceptance signal.