test-driven-development

test-driven-development is a skill for Claude Code, Codex from jxoesneon/Ciel. It costs 20 tokens per session (504 once invoked), scanned A, original, Apache-2.0.

A test-driven development guide that requires writing a failing test before production code, then making it pass and cleaning up the code.

In plain words
What is it for?
Use it to structure behavioural changes through the red, green, and refactor testing cycle.
Why use it?
It reduces the risk of untested behaviour by making expected behaviour explicit before implementation.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it to structure behavioural changes through the red, green, and refactor testing cycle.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/jxoesneon/ciel/test-driven-development
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 jxoesneon/Ciel --skill test-driven-development
Clone the repo
git clone --depth 1 https://github.com/jxoesneon/Ciel

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-driven-development

README.md
[![agentmods](https://agentmods.dev/badge/skills/jxoesneon/ciel/test-driven-development/github.svg)](https://agentmods.dev/skills/jxoesneon/ciel/test-driven-development)
Your own site
<a href="https://agentmods.dev/skills/jxoesneon/ciel/test-driven-development"><img src="https://agentmods.dev/badge/skills/jxoesneon/ciel/test-driven-development/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 test-driven-development

Your own site · 80×15
<a href="https://agentmods.dev/skills/jxoesneon/ciel/test-driven-development"><img src="https://agentmods.dev/badge/skills/jxoesneon/ciel/test-driven-development.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 20 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 504 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 $0.00020 $0.00504
Opus 5 $0.00010 $0.00252
Sonnet 5 $0.00004 $0.00101
Haiku 4.5 $0.00002 $0.00050

Measured 9d ago against content hash c211d4e7fb02, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

test-driven-development 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/test-driven-development/SKILL.md · 69 lines

What it actually says

CIEL ADAPTATION: Test-Driven Development (TDD)

This skill enforces CIEL's "Iron Law" of engineering: no production code without a failing test first.

Integration Context

Adapted from ~/.agents/skills/test-driven-development/. This is a foundation-level mandate for all CIEL-orchestrated engineering.

The Iron Law

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST.

If you wrote code before a test: Delete it. Start over.

The Cycle

  1. RED: Write one minimal test for the desired behavior.
  2. Verify RED: Run the test and confirm it fails for the expected reason.
  3. GREEN: Write the minimal code required to pass the test.
  4. Verify GREEN: Run the test and confirm it passes.
  5. REFACTOR: Clean up the code while keeping the test green.

Orchestration Logic

1. Pre-Task Triage

Before any engineering sub-task, the orchestration skill must ensure a TDD strategy is defined.

2. Council Gate

For high-risk features, the Council of Five (specifically Safety and Evolution) will review the test plan before implementation starts.

3. Verification

A task is not "complete" until:

  • Every new function/method has a corresponding test.
  • All tests pass in the target environment.
  • Output is pristine (no warnings/errors).

Original Documentation preserved at source.

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 · 69 lines · 20 tokens per session scan A c211d4e7fb02

Subscribe to this mod's changes

test-driven-development is a skill published in the GitHub repository jxoesneon/Ciel (1 stars, last pushed 5d ago), licensed Apache-2.0. It adds 20 tokens to every session and 504 once invoked, about $0.0001 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 2026-09-03.