vitest

Add a test property to vite.config.ts with a Vitest types reference, or create a separate vitest.config.ts which takes priority. Use mergeConfig from vitest/config to combine both files when needed.

Call vi.mock with the module path and a factory returning mocked exports; it is hoisted above imports automatically. Use vi.doMock for non-hoisted dynamic mocking, or { spy: true } to keep real implementations while tracking calls.

Vitest shares Vite's config, transformers, and plugins, so tests use the same pipeline as the app with no duplicate configuration. It offers a Jest-compatible API, making most Jest suites portable with minimal changes.

Yes, set environment to jsdom or happy-dom in config, or use a // @vitest-environment comment per file. For real browsers, Vitest Browser Mode runs tests in Chromium, Firefox, or WebKit via Playwright.

Filter by file path as a CLI argument, by test name with -t or --testNamePattern, or by tags with --tags. Use test.only to focus a single test and vitest related to run tests importing specific files.

vi.mock calls are hoisted to the top of the file, so they cannot reference variables declared later. Wrap such variables in vi.hoisted so they are initialized before the mock factory executes.