legacy-code-testing SKILL.md skillA
legacy-code-testing from timwukp/agent-skills-best-practice is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add timwukp/agent-skills-best-practice/legacy-code-testing@v1.0.0Pins v1.0.0 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- timwukp/agent-skills-best-practice
- Path
skills/skills/legacy-code-testing/SKILL.md- Versions recorded
- 1
- Latest version
- v1.0.0, committed Jun 12, 2026
- Size
- 5,331 bytes
- Repository stars
- 12
- License
- MIT
Adds tests to legacy code that has none, safely: characterization tests that pin current behavior (including bugs) before any refactoring, seam identification for breaking untestable dependencies, and a risk-ranked coverage strategy. Use for untested or inherited codebases. Triggers on: "add tests to legacy code", "this code has no tests", "characterization tests", "make this testable", "safe to refactor?", "pin down current behavior", "test this old module before we change it".
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
# Legacy Code Testing Untested code you must change is a trap: you can't refactor safely without tests, and you can't test cleanly without refactoring. The way out is characterization testing — pin down what the code *currently does* (not what it should do), then refactor under that safety net. The golden rule: **before refactoring, tests assert current behavior — even buggy behavior.** A characterization test that "fails" because the code has a bug is wrong; the test must pass against today's code. Log suspected bugs separately for the team to triage. ## Process 1. **Scope and rank.** Identify what actually needs a safety net: code you're about to change, plus its blast radius (callers and shared state). Rank by `change-likelihood × consequence-of-breaking`. Do not attempt whole-codebase coverage — legacy coverage is bought module by module, just-in-time. …
Read the whole file at its exact version.
How to install
mdr add timwukp/agent-skills-best-practice/legacy-code-testing@sha256:4dbab26417de8171The line at the top of this page pins the label v1.0.0, 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_5h6o4henobtc3niu)
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Versions
The registry has recorded 1 version of this file, committed on Jun 12, 2026.
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 (5331 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
timwukp/agent-skills-best-practice · 12 stars · license MIT · pushed 2026-09-16 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_5h6o4henobtc3niu GET https://markdownregistry.com/api/v1/resolve?ref=timwukp/agent-skills-best-practice/legacy-code-testing GET https://markdownregistry.com/api/v1/blob/4dbab26417de8171c43b4a2243d2d2a0e6a59550fef280c5b0d8a813c6486fb4
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.