What is CI? The robot that tests your code every time you push

You change one line, it looks fine, and two days later something far away breaks. Continuous integration (CI) is a robot that prevents that: every time you push code, a fresh computer downloads it, installs it, runs your tests and only then lets it ship.

Push a buggy function in the demo, watch the pipeline stop at the failing test, then fix it and see it go green.