| name | repro-first |
| description | For a real bug, write a failing test (or fixture / matrix row) that reproduces it BEFORE fixing — the test becomes the regression guard. Use when starting on a reported bug, a production incident, or any "it's broken" investigation. Enforces reproduce-before-fix and never-invent-root-causes. |
repro-first
A real bug gets a failing test that reproduces it before the fix lands. The
test is the regression guard for next time. No fix without a repro.
Steps
- Reproduce locally first. Pull evidence for THIS specific failure — the
actual error, log, stack trace, or input. Don't theorize a root cause from
"usually it's X"; get the real signal for this run.
- Write the failing test at the right layer — unit test, integration case,
fixture, or a matrix row — that fails because of the bug. Run it; confirm it
fails for the expected reason (red for the right cause, not a typo).
- Fix the code.
- Confirm green + no collateral. The new test passes, and the surrounding
suite still passes — run the gate that covers the change, not the whole world.
- Keep the test. It ships with the fix in the same change. Don't delete it,
don't mark it skip — it's the guard for the next regression.
Non-negotiables this enforces
- Real bug → repro before fix (rule #34): the failing test lands with the fix.
- Never invent root causes (rule #5): evidence for this run before a theory.
- Reproduce locally before pushing (rule #11).
