# Test First Changes

> Test-first procedure for every behaviour change in Noodle. Use before fixing a bug, changing how code behaves, or acting on a diagnosis made by reading the code; covers the failing test, the fix, the two runs to report, and the CI-safety constraints on tests.

- Skill: `pdparchitect/test-first-changes` (Agent Skill)
- Install (CLI): `npx skillmds@latest add pdparchitect/test-first-changes`
- Raw SKILL.md: https://api.skillmd.com/api/skills/pdparchitect/test-first-changes/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Docs & Writing
- Author: pdparchitect (https://skillmd.com/u/pdparchitect)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/pdparchitect/test-first-changes

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# Behaviour changes are test-first

Do not change behaviour on the strength of reading the code.

1. Write a test that exercises the specific code and fails because of the problem.
2. Run it and see it fail.
3. Make the change.
4. Run the same test and see it pass.
5. Report both runs.

A suspected cause that no test can reproduce is still a hypothesis; say so instead
of changing code.

Tests must not depend on a harness account, a model, the network or timing, so
that they also pass in CI.