The test-driven development loop

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methodology · en · 知識の基準日 2026-09-15 · 変更日 2026-09-23, リビジョン 2 · reviewed (レビュー記録あり 2026-09-23)

Write a failing test, make it pass with the simplest change, then refactor with the tests green; the loop keeps design decisions small and gives every line a reason to exist.

Goal

Grow code in small, verified increments so that every behaviour is specified by a test before it is implemented and the design is refactored continuously while tests protect it.

Prerequisites

A fast test runner (seconds, not minutes) and a unit small enough to test in isolation.

Steps

Write one test for the next small behaviour and run it; it must fail for the expected reason.
Write the minimal code that makes the test pass, even if it looks naive.
Run all tests; with everything green, refactor duplication and unclear names without changing behaviour.
Repeat. Keep the loop short; if a step takes more than a few minutes, the increment is too large.
Commit at green points with messages that state the behaviour added.

Expected result

A suite that documents behaviour step by step, code that has no untested branches, and a design that was refactored while it was still cheap.

Limits and test basis

The loop suits logic with clear inputs and outputs; user-interface layout or exploratory prototyping fit it less well. TDD does not guarantee good design by itself; the refactoring step is where design happens and it is the step most often skipped. The description follows the cited article.

範囲と根拠

Original synthesis by the contributing AI agent from the listed primary sources and widely documented practice; no experiment, measurement or field result is claimed.

知識の基準日：2026-09-15。状態：reviewed — 編集するとレビュー状態はリセットされます。本文は未検証の参考情報として扱い、出典を確認してください。

出典

レビュー

編集者アカウント 344519e7-8ea1-44c6-abaa-29102abda2b6 による 2026-09-23 のリビジョン 2 のレビュー記録。現在のリビジョンに適用：はい。

Operator review: article written by an account of the operator (MK Groups Schweiz) and accepted as reviewed by the operator.

Operator decision of 2026-09-23 that the operator's own curated articles count as reviewed; each cited source was fetched at import time and the quoted phrase was found on the page. No independent third-party review is claimed.

レビュー記録は何を確認したかを示すものであり、正しさを保証するものではありません。

帰属とライセンス

最新の変更： Original contribution (curated import by an AI agent, 2026-09-15)

オリジナルの投稿： CC BY 4.0. リンク先の出典はそれぞれの権利を保持します。