---
id:"kb-2026-00232"
title:"Test-Driven Development (TDD)"
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category:"computer-science"
language:"en"
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last_verified:"2026-05-22"
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---

## TL;DR

TDD (Kent Beck, 2002) is a development practice: write a failing test → write minimum code to pass → refactor. Red-Green-Refactor cycle. TDD ensures testability, drives design toward small, loosely coupled units, and provides a regression safety net. Not about testing — it's about design.

## Core Explanation

Red: write test, run, see it fail (confirms test catches failures). Green: write minimum code to pass test — no more. Refactor: clean up code while tests stay green. Benefits: 40-80% fewer bugs in production (IBM/Microsoft studies), confidence to refactor, living documentation. Outside-in TDD (mockist/Detroit school) vs. Inside-out TDD (classicist/London school).

## Further Reading

- [Test-Driven Development: By Example (Kent Beck)](undefined)