Getting it into your agent
There is no command for this one: it runs only inside a plugin, and the catalogue could not identify which plugin ships it. The source is linked below.
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.
[](https://agentmods.dev/skills/mtnyilmaz/agents/methodology-tdd)<a href="https://agentmods.dev/skills/mtnyilmaz/agents/methodology-tdd"><img src="https://agentmods.dev/badge/skills/mtnyilmaz/agents/methodology-tdd.svg" alt="Measured on agentmods" height="20"></a>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 | $0.00044 | $0.04725 |
| Opus 5 | $0.00022 | $0.02363 |
| Sonnet 5 | $0.00009 | $0.00945 |
| Haiku 4.5 | $0.00004 | $0.00473 |
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 6d 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.
How it starts
The opening of the file, as written. The whole thing — 473 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test-Driven Development
Overview
Write a failing test before writing the code that makes it pass. For bug fixes, reproduce the bug with a test before attempting a fix. Tests are proof — "seems right" is not done. A codebase with good tests is an AI agent's superpower; a codebase without tests is a liability.
The Iron Law
╔══════════════════════════════════════════════════════════╗
║ NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST. ║
║ ║
║ If you didn't watch the test fail, you don't know ║
║ if it tests the right thing. ║
╚══════════════════════════════════════════════════════════╝
No exceptions without explicit user consent. "Just this once" is rationalization — see the table at the end of this document.
Delete Code Written Before Tests
If you wrote implementation code before writing its test — whether from habit, exploration, or a spike — delete it and start over from RED.
- Don't keep it as "reference."
- Don't "adapt" it while writing the test.
- Don't open it in another pane and transcribe.
- Delete means delete.
Why: a test written against existing code tests what the code already does, not what it should do. You'll miss edge cases you never had to discover, because your implementation already made implicit choices for them. The test will pass on first run, which — per the Iron Law — proves nothing.
Exploration is fine. If you need to try an approach before writing tests, do it on a scratch branch / scratch file, then throw it away and implement fresh from the RED test. Keeping exploration code is the single most common way TDD discipline leaks out of an agent session.
When to Use
- Implementing any new logic or behavior
- Fixing any bug (the Prove-It Pattern)
- Modifying existing functionality
- Adding edge case handling
- Any change that could break existing behavior
When NOT to use: Pure configuration changes, documentation updates, or static content changes that have no behavioral impact.
What ships with it
1 file 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.
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.
- 6d ago First seen · 473 lines · 44 tokens per session scan A 106419f35491
test-driven-development is a skill published in the GitHub repository mtnyilmaz/agents (6 stars, last pushed 3mo ago), licensed MIT. It adds 44 tokens to every session and 4,725 once invoked, about $0.0002 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.
Other skills, from other repositories
engram-testing-coverage
TDD and coverage standards for Engram. Trigger: When implementing behavior changes in any package.
nunit-testing
Use when writing or modifying tests in NUnit's own test projects, or when making a behavioral change to production code that needs test coverage. Covers test structure, attribute choice, helper visibility, platform guards, and which test projects are real.
tdd
Test-driven development. Use when the user wants to build features or fix bugs test-first, mentions "red-green-refactor", or wants integration tests.
strict-tdd
Strict RED->GREEN->REFACTOR test-driven development with enforcement. Never write production code before a failing test. Atomic commits per TDD cycle.
tdd
This skill should be used when the user wants to implement features or fix bugs using test-driven development. Enforces the RED-GREEN-REFACTOR cycle with vertical slicing, context isolation between test writing and implementation, human checkpoints, and auto-test feedback loops. Uses multi-agent orchestration with the…
conductor-implement
Execute tasks from a track's implementation plan following TDD workflow.