atdd-mutate skillA
atdd-mutate is agent-read markdown (skill) from swingerman/engineer: 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"..
Indexed from public GitHub and served as immutable, content-addressed versions. Install it pinned to an exact SHA-256 with the mdr CLI, and every file is verified against the hash recorded here before it reaches your agent. The deterministic audit below grades the latest version, and the same file always earns 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@git:20260623.736ab71mdr add swingerman/engineer/atdd-mutate@sha256:bb652f614e7c822dPin to a label to follow the author's releases, or to a sha256 to freeze the exact bytes forever. Either way the resolved hash is written to mdr.lock, and mdr install reproduces it on any machine.
[](https://markdownregistry.com/a/art_wyzduyrf2walacfi)
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Versions
| 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 · 150 stars · license MIT · pushed 2026-09-22 · 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
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