The RED phase of test-driven development: writing tests and confirming that they fail before the implementation exists.

Use it to create test cases from a project cycle plan, assign tests to parallel workers, confirm the tests fail, and then move to the implementation phase.

It prevents tests from passing accidentally and makes the required behavior clear before code is written.

tdd-red — Skill for Claude Code by morodomi

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent

npx skills add morodomi/tdd-skills --skill tdd-red

Clone the repo

git clone --depth 1 https://github.com/morodomi/tdd-skills

Made for: Claude Code.

Or install tdd-core, the plugin that ships this one along with the rest of its 13 skills, 14 agents.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/morodomi/tdd-skills/tdd-red/github.svg)](https://agentmods.dev/skills/morodomi/tdd-skills/tdd-red)

Your own site

<a href="https://agentmods.dev/skills/morodomi/tdd-skills/tdd-red"><img src="https://agentmods.dev/badge/skills/morodomi/tdd-skills/tdd-red/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/morodomi/tdd-skills/tdd-red"><img src="https://agentmods.dev/badge/skills/morodomi/tdd-skills/tdd-red.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 42 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 686 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00042	$0.00686
Opus 5	$0.00021	$0.00343
Sonnet 5	$0.00008	$0.00137
Haiku 4.5	$0.00004	$0.00069

Measured 10d ago against content hash 4cc51064d0a8, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

tdd-red scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 10d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugins/tdd-core/skills/tdd-red/SKILL.md · 95 lines

What it actually says

TDD RED Phase

テストコードを作成し、失敗することを確認する（並列実行がデフォルト）。

Progress Checklist

RED Progress:
- [ ] Cycle doc確認、TODO→WIPに移動
- [ ] テストファイル依存関係分析
- [ ] red-worker並列起動
- [ ] 結果収集・マージ
- [ ] 全テスト実行→失敗確認
- [ ] Cycle doc更新（WIP→DONE相当）
- [ ] GREEN自動実行

禁止事項

実装コード作成（GREENで行う）
テストを通すための実装

Workflow

Step 1: Cycle doc確認

ls -t docs/cycles/*.md 2>/dev/null | head -1

Test ListのTODOからテストケースを選択してWIPに移動。

Step 2: テストファイル依存関係分析

テストケースを対象テストファイル別にグルーピング:

テストファイル	テストケース
tests/AuthTest.php	TC-01, TC-02
tests/UserTest.php	TC-03

原則: 同一テストファイル→同一workerに割り当て（競合回避）

Step 3: red-worker並列起動

Taskツールで tdd-core:red-worker を並列起動:

Task 1: TC-01, TC-02 → tests/AuthTest.php
Task 2: TC-03 → tests/UserTest.php

Step 4: 結果収集・マージ

全workerの完了を待ち、結果を統合。失敗時は該当workerのみ再試行（最大2回）。

Step 5: テスト実行→失敗確認

php artisan test --filter=TestName  # PHP
pytest tests/test_xxx.py -v          # Python

期待: テストが失敗すること（RED状態）

Verification Gate

結果	判定	アクション
テスト失敗	PASS	GREENへ自動進行
テスト成功	BLOCK	テスト条件を見直して再試行

Step 6: 完了→GREEN自動実行

================================================================================
RED完了
================================================================================
テスト作成完了。失敗を確認しました。
GREENフェーズを自動実行します。
================================================================================

Skill(tdd-core:tdd-green) を呼び出して自動的にGREENフェーズへ進行。

Reference

詳細: reference.md
red-worker: ../../agents/red-worker.md

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

reference.md 3.2 KB

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

10d ago First seen · 95 lines · 42 tokens per session scan A 4cc51064d0a8

Subscribe to this mod's changes

tdd-red is a skill published in the GitHub repository morodomi/tdd-skills (8 stars, last pushed 6mo ago), licensed MIT. It adds 42 tokens to every session and 686 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

TDD Testing

tdd-red