atdd-mutate SKILL.md skillA
atdd-mutate from swingerman/engineer is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add swingerman/engineer/atdd-mutate@git:20260623.736ab71Pins git:20260623.736ab71 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- swingerman/engineer
- Path
skills/atdd-mutate/SKILL.md- Versions recorded
- 5
- Latest version
- git:20260623.736ab71, committed Jun 23, 2026
- First version recorded
- May 19, 2026
- Size
- 10,897 bytes
- Repository stars
- 162
- License
- MIT
Use to add a third validation layer to the ATDD workflow — after acceptance tests verify WHAT and unit tests verify HOW, mutation testing verifies the tests actually catch bugs. Triggers — "/mutate", "/kill-mutants", "run mutation testing", "mutate my code", "kill mutants", "check test quality", "find surviving mutants", "run stryker", "run mutmut", "run pitest", "are my tests catching bugs".
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
# Mutation Testing
Add a third validation layer to the ATDD two-stream testing approach.
Acceptance tests verify WHAT, unit tests verify HOW, mutation testing
verifies that the tests **actually catch bugs**.
## Core Concept
Mutation testing introduces deliberate bugs (mutants) into source code,
then runs the test suite. If tests fail, the mutant is **killed** (good).
If tests pass despite the bug, the mutant **survives** (test gap found).
```
Source code → introduce mutation → run tests
├── tests FAIL → mutant killed ✓
└── tests PASS → mutant survived ✗
```
A project with 100% code coverage can still have a 60% mutation score —
meaning 40% of introduced bugs go undetected by the test suite.
## When to Use
Run mutation testing **after both test streams are green**:
1. Acceptance tests pass (WHAT is correct)
2. Unit tests pass (HOW is correct)
3. **Mutation testing** — verify tests actually detect regressions
This is Phase 6 in the team-based ATDD workflow, or a standalone
quality check at any point during development.
## Approach: Custom Mutation Tool (Preferred)
…Read the whole file at its exact version.
How to install
mdr add swingerman/engineer/atdd-mutate@sha256:bb652f614e7c822dThe line at the top of this page pins the label git:20260623.736ab71, 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_wyzduyrf2walacfi)
4 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 5 versions of this file, between May 19, 2026 and Jun 23, 2026, about one every 9 days.
| version | committed | commit | size | audit | |
|---|---|---|---|---|---|
| git:20260623.736ab71 latest | 2026-06-23 | 736ab71 | 10,897 B | A | view · diff |
| git:20260525.78c79de | 2026-05-25 | 78c79de | 10,053 B | A | view · diff |
| git:20260525.947d66d | 2026-05-25 | 947d66d | 10,247 B | A | view · diff |
| v0.6.0 | 2026-05-19 | 20fee2b | 10,262 B | A | view · diff |
| v0.6.0 | 2026-05-19 | 6a6a913 | 8,416 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 (10897 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
swingerman/engineer · 162 stars · license MIT · pushed 2026-10-27 · branch master
API
GET https://markdownregistry.com/api/v1/artifacts/art_wyzduyrf2walacfi GET https://markdownregistry.com/api/v1/resolve?ref=swingerman/engineer/atdd-mutate GET https://markdownregistry.com/api/v1/blob/bb652f614e7c822d903853ab5eb4eb50119b492152621ed1ea4ea01eaa2a4f0c
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.