# Write Failing Test First

> Before fixing any bug, write a test that reproduces it and watch it fail. Use for every bug fix.

- Skill: `archive228/write-failing-test-first` (Agent Skill)
- Install (CLI): `npx skillmds@latest add archive228/write-failing-test-first`
- Raw SKILL.md: https://api.skillmd.com/api/skills/archive228/write-failing-test-first/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: archive228 (https://skillmd.com/u/archive228)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/archive228/write-failing-test-first

---

# Write the Failing Test First
The only proof you fixed a bug is a test that failed before and passes after.
1. Write the smallest test that reproduces the reported behavior.
2. Run it. **Watch it fail** for the right reason (read the assertion, not just red).
3. Now fix the code.
4. Run the test. It passes. Run the FULL suite — you didn't break anything else.
If you can't write the test easily, the architecture is telling you something (tight coupling). Say so.
Never: fix first, test after (you'll write a test that passes regardless). Never: skip the watch-it-fail step.