tdd

tdd is a skill for Claude Code from jhlee0409/omni-harness-kit. It costs 105 tokens per session (425 once invoked), scanned A, original, MIT.

A test-first coding workflow based on the red–green–refactor cycle: write a failing test, make it pass with the smallest change, then clean up the code.

In plain words
What is it for?
Use it when adding a feature or fixing a bug in library, backend, or command-line code. It guides you through writing, running, and checking each test and implementation step.
Why use it?
It prevents implementation from getting ahead of clearly defined behavior and provides evidence that each change works.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

Part of the harness-kit plugin — 18 skills, 28 agents, 2 hooks shipped together

Good fit Use it when adding a feature or fixing a bug in library, backend, or command-line code. It guides you through writing, running, and checking each test and implementation step.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/jhlee0409/omni-harness-kit/tdd
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 jhlee0409/omni-harness-kit --skill tdd
Clone the repo
git clone --depth 1 https://github.com/jhlee0409/omni-harness-kit

Made for: Claude Code.

Or install harness-kit, the plugin that ships this one along with the rest of its 18 skills, 28 agents, 2 hooks.

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/jhlee0409/omni-harness-kit/tdd/github.svg)](https://agentmods.dev/skills/jhlee0409/omni-harness-kit/tdd)
Your own site
<a href="https://agentmods.dev/skills/jhlee0409/omni-harness-kit/tdd"><img src="https://agentmods.dev/badge/skills/jhlee0409/omni-harness-kit/tdd/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.

agentmods 80×15 button for tdd

Your own site · 80×15
<a href="https://agentmods.dev/skills/jhlee0409/omni-harness-kit/tdd"><img src="https://agentmods.dev/badge/skills/jhlee0409/omni-harness-kit/tdd.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 105 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 425 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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00105 $0.00425
Opus 5 $0.00053 $0.00212
Sonnet 5 $0.00021 $0.00085
Haiku 4.5 $0.00011 $0.00042

Measured 9d ago against content hash b58a927e1dc2, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, 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 9d 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.

skills/tdd/SKILL.md · 35 lines

What it actually says

tdd

One behavior at a time. Never write implementation before a failing test for it.

The loop

  1. 🔴 Red — write the smallest test that expresses the next behavior. Run it with the repo's runner (the verify_command / test command from .claude/harness-kit.json). Confirm it FAILS, and fails for the RIGHT reason (asserting the missing behavior — not a typo / import error). A test that passes immediately, or fails for the wrong reason, tells you nothing.
  2. 🟢 Green — write the MINIMUM implementation to make it pass. No extra features, no speculative generality. Run the test; confirm green.
  3. 🔵 Refactor — with the test green, clean up (names, duplication, shape) without changing behavior. Re-run; stay green.

Discipline

  • Structural and behavioral changes never mix in one commit (Tidy First).
  • Keep the red→green step small — minutes, not an hour. If it's big, the test is too coarse; split it.
  • A real run is the evidence: show the runner output (red, then green), not a claim.
  • Mandatory for library / backend / CLI code, where there's no UI to eyeball.
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. 9d ago First seen · 35 lines · 105 tokens per session scan A b58a927e1dc2

Subscribe to this mod's changes

tdd is a skill published in the GitHub repository jhlee0409/omni-harness-kit (2 stars, last pushed 1mo ago), licensed MIT. It adds 105 tokens to every session and 425 once invoked, about $0.0005 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.

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