characterization-test-writer SKILL.md skillA
characterization-test-writer from skillmedev/skills is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add skillmedev/skills/characterization-test-writer@git:20261005.bea4ea5Pins git:20261005.bea4ea5 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- skillmedev/skills
- Path
skills/characterization-test-writer/SKILL.md- Versions recorded
- 3
- Latest version
- git:20261005.bea4ea5, committed Oct 5, 2026
- First version recorded
- Jul 5, 2026
- Size
- 6,581 bytes
- Repository stars
- 19
- License
- MIT
Writes pinning and characterization tests that lock in the current behavior of untested legacy code - bugs included - before a refactor, so any later behavior change trips an alarm. Use when someone says "I need a safety net before refactoring this", "this module has no tests and I have to change it", "capture what this function does today", or the correct behavior is simply whatever the code does now. Do NOT use for writing tests for new behavior built red-green - use tdd-expert instead; do…
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
# Characterization Test Writer Pin what legacy code currently does - bugs included - so a refactor that changes behavior fails loudly instead of silently. The costly mistake this prevents is the "clean" refactor that quietly changes an output nobody noticed was load-bearing, discovered weeks later in production. A characterization test records reality; it never judges it. ## Operating procedure Order matters: the seam must exist before you can capture output, output must be captured before you can stabilize it, and coverage is only measurable once tests run. ### Step 1: Gather inputs - The exact function/module about to change, and the refactor's blast radius - which code paths will the change touch? Only those need pinning. - The dependency list: database, clock, RNG, network, filesystem, globals, environment. Each is a nondeterminism source to control in Step 4. - Any recorded production inputs or logs available for replay. Label assumptions about "typical inputs" as guesses. ### Step 2: Find the smallest seam …
Read the whole file at its exact version.
How to install
mdr add skillmedev/skills/characterization-test-writer@sha256:b48fdc1a25a98778The line at the top of this page pins the label git:20261005.bea4ea5, 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.
[](https://markdownregistry.com/a/art_3nqc2eusa3vqiyed)
2 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 3 versions of this file, between Jul 5, 2026 and Oct 5, 2026, about one every 46 days.
| version | committed | commit | size | audit | |
|---|---|---|---|---|---|
| git:20261005.bea4ea5 latest | 2026-10-05 | bea4ea5 | 6,581 B | A | view · diff |
| git:20260705.a28c4ce | 2026-07-05 | a28c4ce | 6,531 B | A | view · diff |
| git:20260705.acb5571 | 2026-07-05 | acb5571 | 6,561 B | A | view |
Audit of the latest version
- pass: Frontmatter block present
- pass: Frontmatter declares a name
- pass: Frontmatter declares a description
- pass: Size between 200 bytes and 200 KB (6581 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
skillmedev/skills · 19 stars · license MIT · pushed 2026-10-13 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_3nqc2eusa3vqiyed GET https://markdownregistry.com/api/v1/resolve?ref=skillmedev/skills/characterization-test-writer GET https://markdownregistry.com/api/v1/blob/b48fdc1a25a98778cb788156ed1a533916b4395561248abd56c766c8b040935f
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.
Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.