I built a demo script to show off a project. It failed on step 2 — and in doing so, it found a real bug that had been sitting in the codebase the whole time, invisible to a fully green test suite. This is a short technical report on what happened, why the tests missed it, and what it taught me ...
Source: [Dev.to](https://dev.to/xbill/my-demo-script-found-a-production-bug-on-its-first-run-a-tiny-post-mortem-k35)