tdd

Test-driven development (TDD) is writing tests before code to reduce defects and enable safer refactoring. The Red-Green-Refactor cycle involves writing a failing test (red), implementing the simplest code to pass it (green), then refactoring while keeping tests green.

Apply TDD using Jest for TypeScript and pytest for Python. Write failing unit tests first, run your test runner to confirm failure, implement minimal code to pass, then refactor. Both frameworks integrate with standard CI workflows.

TDD naming conventions clarify test intent, while AAA patterns structure tests into Arrange (setup), Act (execute), and Assert (verify) sections. These practices accelerate delivery and maintain test readability across TypeScript and Python projects.

Yes, TDD requires only standard test runners. npm test for TypeScript/Jest and pytest for Python are sufficient to implement Red-Green-Refactor guidance, test naming conventions, and fixture patterns without additional external dependencies.

Refactoring within TDD improves code maintainability and design while tests verify correctness. Keeping tests green during refactoring ensures changes don't introduce bugs, creating a disciplined development approach that reduces defects over time.

TDD's three laws ensure you write failing tests before code, write only enough code to pass tests, and refactor only when tests are green. This discipline prevents over-engineering and keeps implementation focused on requirements.