# testing-changes

Defines test requirements for code changes, enforcing regression tests for bug fixes, edge-case coverage, and strict checks against empty test diffs.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 17900 installs · ★ 6
- Author: riekelt
- License: not stated · policy=link-only · description only; the file stays with the author
- Source: https://github.com/riekelt/principal-engineer/tree/HEAD/plugins/principal-engineer/skills/testing-changes/SKILL.md
- Updated: 2026-09-11
- HTML: https://affpapa.org/en/nevibecode/skills/testing-changes

## What it does

This skill determines what tests a pull request owes whenever software behavior changes. If a pull request modifies system logic without updating test files, the skill treats the empty test diff as a review defect. Bug fixes must come with a regression test showing a failure on the unfixed code before turning green. Tests must isolate the defect.

Happy paths alone are not enough. The skill directs agents to cover failure branches and surfaced edge cases, requiring a targeted verify command for each task. Silencing failing checks by skipping or weakening assertions is forbidden. When an assertion breaks, authors must fix the root cause instead of ignoring it.

You need the `principal-engineering` skill installed beforehand as required background. Without it, the agent cannot map invariants or risk tiers to project critical paths. The skill does not mandate strict test-first workflows, leaving the creation order to developer preference.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add riekelt/principal-engineer --skill testing-changes -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/testing-changes/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/testing-changes/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add riekelt/principal-engineer --skill testing-changes -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/testing-changes/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add riekelt/principal-engineer --skill testing-changes -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/testing-changes/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install riekelt/principal-engineer testing-changes
```

2. **Manually: put the files in place**
- File: `.github/skills/testing-changes/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add riekelt/principal-engineer --skill testing-changes -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/riekelt/principal-engineer --path plugins/principal-engineer/skills/testing-changes
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/testing-changes/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add riekelt/principal-engineer --skill testing-changes -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/riekelt/principal-engineer/tree/HEAD/plugins/principal-engineer/skills/testing-changes/SKILL.md

## When to use it
- review whether a pull request includes sufficient tests for behavior changes
- write a reproducible regression test that fails before a bug fix is applied
- define an isolated verification command for a targeted task
- verify invariants and reconciliation logic on critical data paths

## Example prompts
- Review this diff and tell me what tests are missing for the behavior changes
- Draft a regression test for the checkout failure that fails on the unfixed code
- What test coverage does this refactoring task owe before merging?

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From the same set: [riekelt/principal-engineer](https://affpapa.org/en/nevibecode/by/riekelt/principal-engineer.md) — 4 cards

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