Test-Driven Development (TDD) Guide

Test-driven development (TDD) is a methodology where you write failing tests before implementing features, ensuring correct behavior and preventing regressions. It structures work into three phases: RED (write a failing test), GREEN (implement the simplest code to pass), and REFACTOR (improve while keeping tests green).

Start by writing a minimal failing test for your feature. Next, implement the simplest code necessary to pass that test. Finally, refactor your code to improve quality while ensuring all tests remain green. Repeat this cycle for each feature, bug fix, and refactoring effort.

The iron law of TDD states that production code requires a failing test first. This discipline ensures every feature has test coverage from inception, catches bugs early, and maintains verification checkpoints throughout development at unit, integration, and system levels.

Use verification checkpoints at each stage of the red-green-refactor cycle. Confirm your test fails before writing production code, verify it passes after implementation, and validate that refactoring maintains green tests. This prevents false positives and ensures test quality.

Yes. TDD applies across feature development, bug fixes, and refactoring scenarios. For bugs, write a failing test that reproduces the issue, fix the code, then refactor. For refactoring, ensure existing tests pass, improve the code, and verify tests remain green.

TDD enforces discipline by requiring tests before code, catching defects early and preventing regressions. This test-first approach ensures requirements are clear, code is verifiable at each cycle stage, and quality is maintained through continuous verification checkpoints.