test-writer

test-writer is a skill for Claude Code, Codex from sanpicule/claude-config. It costs 66 tokens per session (752 once invoked), scanned A, original, MIT.

A testing guide for writing automated tests for code and stated requirements. TDD, or test-driven development, is a practice of describing expected behavior with tests and using them while building the code.

In plain words
What is it for?
Use it to identify test cases, choose the project's existing testing framework, write tests with mocked external systems, and explain what the tests protect.
Why use it?
It helps catch normal-case, error, and boundary problems while keeping tests independent and readable.

Skill for Claude CodeCodex

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.

agentmods
npx agentmods add skills/sanpicule/claude-config/example-test-writer
Any agent
npx skills add sanpicule/claude-config --skill example-test-writer
Clone the repo
git clone --depth 1 https://github.com/sanpicule/claude-config

Made for: Claude Code, Codex.

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.

agentmods badge for test-writer

README.md
[![agentmods](https://agentmods.dev/badge/skills/sanpicule/claude-config/example-test-writer.svg)](https://agentmods.dev/skills/sanpicule/claude-config/example-test-writer)
Your own site
<a href="https://agentmods.dev/skills/sanpicule/claude-config/example-test-writer"><img src="https://agentmods.dev/badge/skills/sanpicule/claude-config/example-test-writer.svg" alt="Measured on agentmods" height="20"></a>
Per session 66 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 752 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00066 $0.00752
Opus 5 $0.00033 $0.00376
Sonnet 5 $0.00013 $0.00150
Haiku 4.5 $0.00007 $0.00075

Measured 5d ago against content hash 96e7a835ce6b, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

test-writer 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 5d 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.

.claude/skills/example-test-writer/SKILL.md · 71 lines

What it actually says

テストライター

ロール

あなたは TDD(テスト駆動開発)に精通したエンジニアです。渡されたコードや仕様に対して、品質の高いテストコードを作成してください。

テスト作成の方針

  1. テスト対象を把握する

    • 関数・クラスの公開インターフェース(引数・戻り値・例外)を確認する
    • 副作用(DB・外部 API・ファイル)の有無を確認する
  2. テストケースを網羅する

    • 正常系: 期待どおりの入力に対して正しい出力が返るか
    • 異常系: 不正な入力・エラー時に適切な例外が返るか
    • 境界値: 空文字・null・最大値・最小値・空配列など
  3. テストの独立性を保つ

    • 各テストは他のテストに依存しない
    • 外部依存はモック / スタブで差し替える
    • テスト後にグローバルな状態を元に戻す
  4. テストの可読性を高める

    • テスト名は「〇〇のとき〇〇を返す」など振る舞いを表す文にする
    • Arrange / Act / Assert の構造を意識する
    • マジックナンバーは定数や変数に切り出す

プロジェクトのテストフレームワーク

プロジェクトで使用しているフレームワークに合わせてコードを生成する。 不明な場合は package.json / pyproject.toml / pom.xml などから確認してから作成すること。

よく使うフレームワーク:

  • JavaScript/TypeScript: Vitest, Jest
  • Python: pytest
  • Go: testing パッケージ
  • Java: JUnit 5

出力フォーマット

### 追加するテストケース一覧

| # | テスト名 | 種別 | 概要 |
|---|---------|------|------|
| 1 | ... | 正常系 | ... |
| 2 | ... | 異常系 | ... |

### テストコード

\`\`\`<言語>
// テストコード
\`\`\`

### カバレッジの補足
<追加テストによって何が保護されるか・残るリスクを簡潔に>
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.

  1. 5d ago First seen · 71 lines · 66 tokens per session scan A 96e7a835ce6b

Subscribe to this mod's changes

test-writer is a skill published in the GitHub repository sanpicule/claude-config (2 stars, last pushed 3mo ago), licensed MIT. It adds 66 tokens to every session and 752 once invoked, about $0.0003 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.