What is tdd-workflow?

A test-driven development workflow, or TDD, where a failing automated test defines the intended behavior before production code is changed. The workflow then checks that the fix passes the relevant tests and an edge case.

Use it for features, bug fixes, and refactors when an automated test can verify the behavior, including defining the test contract and running the affected test suite.

It turns a requirement into concrete proof and helps show that a change fixes the real problem rather than only matching one example. It also sets clear boundaries for the implementation.

tdd-workflow — Skill for Codex by ashermahonin/agentic-skills

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 ashermahonin/agentic-skills --skill tdd-workflow

Clone the repo

git clone --depth 1 https://github.com/ashermahonin/agentic-skills

Made for: 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/ashermahonin/agentic-skills/tdd-workflow/github.svg)](https://agentmods.dev/skills/ashermahonin/agentic-skills/tdd-workflow)

Your own site

<a href="https://agentmods.dev/skills/ashermahonin/agentic-skills/tdd-workflow"><img src="https://agentmods.dev/badge/skills/ashermahonin/agentic-skills/tdd-workflow/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/ashermahonin/agentic-skills/tdd-workflow"><img src="https://agentmods.dev/badge/skills/ashermahonin/agentic-skills/tdd-workflow.svg" alt="Reviewed on agentmods" width="80" 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 641 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	$0.00066	$0.00641
Opus 5.5	$0.00026	$0.00256
Sonnet 5.5	$0.00013	$0.00128
Haiku 4.5	$0.00007	$0.00064

Measured 2mo ago against content hash 201cb83dfa69, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

tdd-workflow 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 2mo 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.

agentic/skills/tdd-workflow/SKILL.md · 61 lines

How it starts

The opening of the file, as written. The whole thing — 61 lines — stays where its author put it; the contents beside it link to each section on GitHub.

TDD Workflow

Purpose

Turn an acceptance criterion into executable evidence before production code changes. This skill owns the test contract and proof; service-implementation owns production edits.

When a route also includes service-implementation, this skill owns the test contract, red evidence, anti-overfit criteria, and reproduction commands. service-implementation owns the production code change under that contract. When this skill is used alone, it may execute the full red/green/refactor loop itself.

Change context

Read references/tdd-loop.md.
State the changed behavior and the acceptance criterion it satisfies.
Choose the lowest test level that can prove the behavior without mocking away the risk.
Confirm the repository's test command and current framework behavior before writing the test.

Change method

Write one test for one observable behavior and run it before changing production code.
Confirm that it fails because the behavior is missing or wrong, not because the test setup is broken.
Hand service-implementation the expected behavior, owned files, prohibited shortcuts, and exact verification command.
After implementation, run the new test and the affected suite. Do not weaken assertions to obtain a pass.
Add one meaningful boundary, invalid-input, or failure-path case that the first test did not cover.
Refactor only while the affected suite remains green; use engineering-quality when structure or maintainability is part of the change.
Map each covered acceptance criterion to a test file and list anything still unproved.

Engineering constraints

Use current test-runner documentation when syntax, fixtures, matchers, or isolation behavior is uncertain.
Record what the chosen test level proves and what it cannot prove.
Do not require test-first work when no automated test can provide useful evidence; document the alternative verification path instead.
Never delete, skip, or weaken an existing test solely to make a change pass.

Read the full file on GitHub · 61 lines

Files

What ships with it

2 files 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.

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.

2mo ago First seen · 61 lines · 66 tokens per session scan A 201cb83dfa69

Subscribe to this mod's changes

tdd-workflow is a skill published in the GitHub repository ashermahonin/agentic-skills (10 stars, last pushed 2mo ago), licensed MIT. It adds 66 tokens to every session and 641 once invoked, about $0.0003 per session on Opus 5.5. 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-workflow next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
tdd-workflowashermahonin/agentic-skills	Skill	10	2mo ago	MIT	A	66	Codex
engram-testing-coverageGentleman-Programming/engram	Skill	7.8k	yesterday	MIT	A	25	Claude Code, Codex
principle-test-behavior-not-implementationmichael-denyer/pstack-claude	Skill	4.1k	yesterday	MIT	A	50	Claude Code
tddcodewithmukesh/dotnet-claude-kit	Skill	805	2d ago	MIT	A	81	Claude Code
nw-ddd-eventsourcingnWave-ai/nWave	Skill	631	yesterday	MIT	A	38	Claude Code
nw-fp-clojurenWave-ai/nWave	Skill	631	yesterday	MIT	A	25	Claude Code
nw-leanux-methodologynWave-ai/nWave	Skill	631	yesterday	MIT	A	37	Claude Code