test-driven-development

Test-driven development writes failing tests before implementation, ensuring tests verify actual behavior rather than implementation details. You write a test that fails, implement minimal code to pass it, then refactor—this RED-GREEN-REFACTOR cycle prevents bugs and guides design decisions across npm, cargo, pytest, and go test projects.

Yes. Test-driven development integrates with common test runners including npm, pytest, cargo, and go test, letting you apply the same RED-GREEN-REFACTOR discipline across JavaScript, Python, Go, and Rust codebases while maintaining consistent test coverage and quality.

After your test passes (green phase), refactor your code to improve design and remove duplication while keeping tests passing. TDD's refactor stage ensures changes maintain correctness and prevents regressions, building confidence in quality through continuous verification.

Writing tests after code often creates tests biased by implementation, missing edge cases and real behavior verification. Test-driven development enforces failing tests first, requiring you to see tests fail to confirm they actually verify behavior, preventing false confidence and catching bugs earlier.

Yes. TDD applies to new features, bug fixes, and refactors across languages. For bug fixes, you write a failing test reproducing the bug, then implement the fix; for refactors, tests verify behavior stays correct, guiding design improvements with automated verification.

TDD enforces a failing-test-first requirement and includes anti-rationalization rules to counter common excuses for skipping this step. Skipping the failure verification stage defeats TDD's core benefit: confirming tests actually check behavior, not just passing by accident.