Testing

Kinds of tests, Vitest, Testing Library and Playwright.

1. 1Why and what we testAutomated tests, Arrange-Act-Assert, kinds of tests and what's worth testing.
2. 2Vitest: unit testsdescribe/test/expect, the right matchers, mocks and fake timers.
3. 3Testing Library: components like a userQueries by role and label, get/query/find, user-event.
4. 4Playwright: end-to-end testsA real browser, locators, auto-waiting and what's worth testing E2E.