n8n/scripts/mutation-health/DEMO-HANDOVER.md

Demo handover: stacked PR on #30956

Use this prompt to drive the mutant-fix loop end-to-end and open a stacked PR that demonstrates the trial.

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Prompt

I want to demo the mutation-health mutant-fix loop from PR #30956. Drive the whole flow from a fresh branch and open a stacked PR.

Base branch: devp-stryker-mvp-spike (the PR's branch — not master yet).

Steps:

1. git fetch origin && git checkout devp-stryker-mvp-spike && git pull && git checkout -b demo/strengthen-<file-basename>

2. Query the live ledger to find the lowest-score red file:

   curl -sS 'https://internal.users.n8n.cloud/webhook/mutation-health-ledger?package=n8n-workflow' \
     | jq '.ledger | map(select(.status == "red")) | sort_by(.last_score | tonumber) | .[0]'
   

   Use whatever it returns. As of 2026-05-22, that's src/workflow-checksum.ts at 38.64% — but check live state first.

3. Run the local mutation-testing skill on that file: /mutant-score packages/workflow/src/<picked-file>

   Confirm the output JSON shows the score and a list of survivors with mutator + location + covering tests.

4. Run the strengthen skill: /mutant-fix

   It'll triage survivors (HIGH/MODERATE/LOW), edit the covering test file with targeted assertions, and re-run mutant-score to verify the score climbed. Max 5 survivors per pass.

5. Review the diff yourself: git diff packages/workflow/test/

   Sanity-check each new assertion. Reject anything that's mocking-the-mock, asserting trivia, or pinning behaviour the source doesn't actually have. The skill is supposed to refuse to fabricate but humans verify.

6. If you want to push further, re-invoke /mutant-fix for the next 5 survivors. Or move on.

7. Final verification: /mutant-score packages/workflow/src/<picked-file>

   Capture the before/after score for the PR body.

8. Push and open a stacked PR against devp-stryker-mvp-spike (not master):

   git push -u origin demo/strengthen-<file-basename>
   gh pr create --draft --base devp-stryker-mvp-spike \
     --title "test(core): strengthen <file-basename> assertions (demo) (no-changelog)" \
     --body "<see template below>"
   

PR body template:

## Summary

Demo PR for #30956. Drives the `mutant-fix` loop against `packages/workflow/src/<file>` to show the trial loop end-to-end.

**Before**: <X>% mutation score, <N> survivors
**After**:  <Y>% mutation score, <M> survivors

Survivors addressed (with rationale):
1. <mutator at location> — added <which assertion> to <which existing test>
2. ...

## Test plan
- [ ] `pnpm mutate packages/workflow/src/<file>` reproduces the post-score locally
- [ ] `pnpm --filter=n8n-workflow test test/<file>.test.ts` passes
- [ ] Each new assertion has a clear "this would have caught X bug" justification

Goals of the demo:

• Reviewer sees a real diff with surgical assertion edits, not big-bang test rewrites
• The before/after numbers are reproducible (pnpm mutate gives the same answer to anyone)
• The skill refused to fabricate or split low-leverage survivors out — what landed is what mattered

What NOT to do:

• Don't rewrite whole test files. The skill should only add/extend covering tests.
• Don't bypass the verify step. Every change must be backed by a re-run that shows the score moved.
• Don't auto-merge. This is a draft demo; the reviewer takes it forward.

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Why this is a good first PR for a reviewer

• Small (a handful of assertion lines)
• Numerically verifiable (run pnpm mutate yourself, see the same number)
• Demonstrates the full loop without committing to the AI auto-PR pipeline yet
• Stacked on devp-stryker-mvp-spike so the loop's machinery is already on the branch