Use when writing production code that needs tests -- new features, bug fixes, refactoring. Enforces RED-GREEN-REFACTOR before implementation.
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
<objective>
TDD enforces the Iron Law -- no production code without a failing test first -- through a strict RED-GREEN-REFACTOR loop: detect the stack and test framework, write one failing test for the next behavior, verify it fails for the *expected* reason (not a syntax error or missing fixture), write the simplest code that passes it, verify the full suite is green, refactor while staying green, then repeat for the next behavior.
It never skips a VERIFY step -- a test that passes on first run proves nothing and must be investigated, not accepted.
</objective>
# TDD Skill
Write the test first. Watch it fail. Write minimal code to pass.
## The Iron Law
**No production code without a failing test first.**
Every line of production code must be justified by a test that failed without it.
No exceptions. No shortcuts. No "I'll test after."
---
## Agent Workflow
```
1. DETECT -> Identify stack, test framework, existing test patterns
2. RED -> Write ONE failing test for the next behavior
3. VERIFY -> Run test, confirm it fails for the EXPECTED reason
…
The line at the top of this page pins the label git:20260729.3b91eed, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
A 17 of 17 checks passed. Fixed automatic checks with no AI involved, so the same checks give the same answer every run.
pass: Frontmatter block present
pass: Frontmatter declares a name
pass: Frontmatter declares a description
pass: Size between 200 bytes and 200 KB (3036 bytes)
pass: No zero-width or bidi control characters
pass: No instruction hidden inside an HTML comment
pass: No link to an exfiltration or paste host
pass: No credential-shaped string
pass: No instruction to send local credentials anywhere
pass: No text hidden with inline styles
pass: No prompt-injection phrasing
pass: No curl or wget piped into a shell
pass: No recursive delete of root, home or parent
pass: No instruction to read or print local credentials
pass: No base64 blob over 200 characters
pass: No link to a raw IP address
pass: No script tag
Source
GitHub
fusengine/agents · 34 stars · license MIT · pushed 2026-10-30 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_rm2cyppvqcnj2nl3
GET https://markdownregistry.com/api/v1/resolve?ref=fusengine/agents/tdd
GET https://markdownregistry.com/api/v1/blob/9868b22627b6237251a19dbe5b5f915a3668058b1f8f76056fc90275631b2e8c
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
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