Testing in CI (What Runs on Every Push)

CI is a server that automatically runs your test suite on every push and pull request, so broken code can't quietly reach main - here's the mental model, what a run actually does, and how to keep it trustworthy.

1. What CI Testing Actually Is CI is a server that automatically runs your full test suite on every push and pull request; the green check on a PR means those tests passed on a clean machine, which is why it beats 'it passed on my machine'.
2. Inside the Pipeline A CI run checks out your code on a clean machine, installs dependencies, runs lint and tests (sometimes across several versions or OSes), and reports pass or fail; here's an annotated GitHub Actions config and a real run log, focused on the test step.
3. Keeping CI Trustworthy Flaky tests - ones that pass or fail randomly - are what destroy CI's value, because people start ignoring red; here's why flakiness happens (timing, order, shared state), how to keep the suite fast and reliable, and how required checks protect main.