One W3C concept which I didn’t fully wrap my head around till recently is the idea of a test suite. It is a set of files that each test a certain property or aspect of a specification (… being things like HTML, CSS, or SVG).
For example, there could be a test which makes sure that a browser can render bold text correctly. That’s all it’d do. You’d view the file in the browser and you can quickly tell that whether the browser passed or failed.
There are a bunch of test suites…
Test suites are important so that you can test that the specification was implemented properly. What good is a spec unless it’s been implemented somewhere and implemented consistently?