tdd

tdd is a skill for Claude Code, Codex from michael-denyer/pstack-claude. It costs 52 tokens per session (700 once invoked), scanned A, a copy of tdd, MIT.

A method for fixing a bug by first writing a test that reproduces it, then changing the code until the test passes. TDD means test-driven development, a practice of using tests to define expected behavior.

In plain words
What is it for?
Use it when a bug has a small, clear test case. It recommends skipping a new test when testing would require broad, slow, or unreliable setup.
Why use it?
It helps prevent the same bug from returning and confirms that the fix addresses the intended behavior.

Skill for Claude CodeCodex

Part of the pstack plugin — 52 skills, 2 agents, 1 hook shipped together

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/michael-denyer/pstack-claude/tdd
Any agent
npx skills add michael-denyer/pstack-claude --skill tdd
Clone the repo
git clone --depth 1 https://github.com/michael-denyer/pstack-claude

Made for: Claude Code, Codex.

Or install pstack, the plugin that ships this one along with the rest of its 52 skills, 2 agents, 1 hook.

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 tdd

README.md
[![agentmods](https://agentmods.dev/badge/skills/michael-denyer/pstack-claude/tdd.svg)](https://agentmods.dev/skills/michael-denyer/pstack-claude/tdd)
Your own site
<a href="https://agentmods.dev/skills/michael-denyer/pstack-claude/tdd"><img src="https://agentmods.dev/badge/skills/michael-denyer/pstack-claude/tdd.svg" alt="Measured on agentmods" height="20"></a>
Per session 52 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 700 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 95% copy Near-identical to another mod 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 $0.00052 $0.00700
Opus 5 $0.00026 $0.00350
Sonnet 5 $0.00010 $0.00140
Haiku 4.5 $0.00005 $0.00070

Measured 4d ago against content hash f5970d98aed9, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

tdd 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 4d 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.

Origin

This is a copy

95% identical to tdd — 2 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

plugins/pstack/skills/tdd/SKILL.md · 45 lines

How it starts

The opening of the file, as written. The whole thing — 45 lines — stays where its author put it; the contents beside it link to each section on GitHub.

TDD Bug Fix

When fixing a bug with a clear, cheap test path, make the broken behavior executable before changing production code. The goal is a focused regression test that fails before the fix and passes after it.

Do not force a test when it would be impractical. If the available test would require broad harness setup, brittle mocks, slow end-to-end infrastructure, production-only state, vague reproduction steps, or large unrelated fixture churn, skip adding a new test and use the closest useful verification instead.

Workflow

  1. Understand the bug. Identify the intended behavior, current behavior, affected path, and smallest observable reproduction.
  2. Choose the narrowest executable check. Prefer the closest unit, component, integration, or regression test already used for that codepath. If no practical test path is obvious, do not create one from scratch just to satisfy the workflow.
  3. Write the failing test first. Add the smallest focused test that would have caught the bug. The test should encode intended behavior, not mirror the current implementation.
  4. Run the new test before fixing. Confirm it fails for the intended reason. If it passes or fails for an unrelated reason, correct the test or reproduction before editing the implementation.
  5. Fix the bug. Make the smallest production change that satisfies the intended behavior while preserving nearby contracts.
  6. Rerun the regression test. Confirm the test now passes.
  7. Run nearby validation. Run relevant adjacent tests, type checks, lint, or scenario checks when the change has broader risk.

If a Failing Test Is Impractical

Do not silently skip the regression step. Before fixing, explicitly explain why a failing test is impossible or not worth the cost, then choose the closest executable regression check available. Examples include a targeted script, manual reproduction command, browser automation, snapshot comparison, log assertion, or focused integration check.

Read the full file on GitHub · 45 lines

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. 4d ago First seen · 45 lines · 52 tokens per session scan A f5970d98aed9

Subscribe to this mod's changes

tdd is a skill published in the GitHub repository michael-denyer/pstack-claude (195 stars, last pushed yesterday), licensed MIT. It adds 52 tokens to every session and 700 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. It is 95% identical to tdd, differing in 2 lines, and is treated as a copy.

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