Regression guard

Skill dennisonbertram/developer-skill-pack/skills/regression-guard

Post-fix test-coverage analysis. Reviews a just-landed fix, generates targeted unit and regression tests, audits how the bug could have been caught earlier. Use after a fix is merged, when asked to 'add regression tests', 'pay off test debt', 'guard against regression', or 'ensure this doesn't happen again'.From its SKILL.md

Install

npx -y skills add dennisonbertram/developer-skill-pack --skill regression-guard

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

One thing to look at

1 stars1 stars. Stars are a popularity signal and not a quality one, but at this level it is likely that nobody has read this closely except its author, and you would be relying on your own review.

SKILL.md

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Regression Guard

Post-fix test-debt payoff loop. Takes the git diff of a recent fix as input and generates targeted tests to prevent the bug from returning.

Usage

/regression-guard [commit-range]

If no commit range is specified, uses HEAD~3..HEAD.

Step 1 — Review What Was Fixed

Build a structured summary from git:

git log --oneline -10
git diff HEAD~3..HEAD
git log -1 --format=%B

Produce:

What broke — the failure mode
What changed — specific code paths
Files and functions touched
Issue/PR reference

Step 2 — Generate Unit Tests

Write the smallest set of unit tests that lock in the correct behavior:

tests/unit/<area>/<fix-slug>.test.<ext>

Rules:

Each test must be red when reverted against the pre-fix state
Cover the happy path AND the corrected edge cases
State which assertion would be red if reverted

Step 3 — Generate Regression Tests

Write regression tests that construct the exact pre-fix state:

tests/regression/<area>/<fix-slug>-regression.test.<ext>

Rules:

Include a top-of-file comment identifying the pre-fix state and symptom
The test must pass the full check suite with no manual edits

Step 4 — Audit: Could This Have Been Caught Earlier?

Answer honestly. Pick the most relevant gap category:

Missing boundary test — contract assertion at a module seam
Missing negative test — error path never exercised
Non-hermetic test harness — shared state leaked between tests
Missing integration coverage — only reproduced under production shape
Contract drift — upstream contract widened/narrowed without downstream rebase

For each gap, write a concrete, actionable suggestion. No generic "add more tests."

Step 5 — Recommend Integration Testing Additions

Name:

The specific test command to extend
The specific file to add a test into (or create)
A concrete test stub that would have caught the bug

Output Report

Write to docs/investigations/<date>-regression-guard-<fix-slug>.md:

Fix summary
Generated unit tests (file paths + descriptions)
Generated regression tests (file paths + pre-fix state each reconstructs)
"Could this have been caught earlier?" diagnosis
Integration testing recommendations
Baseline comparison table

Ship as a Draft PR

Create a new branch
Commit the generated test files and output report
Open a draft PR against main
Never push directly to main