Make a check fail on purpose before trusting it
A test that says 'all clear' means nothing until you've seen it catch a planted problem.
how it works
Plant a canary, watch it get caught, remove it, watch it go quiet; three same-shape false-clean checks in one day motivated it.
Technique: A pattern or hard-won lesson, written down so it isn't learned twice.
The code for this one lives in a private repo. This page explains the idea so you can build your own.