vitest

Use vi.mock with a factory function, which is hoisted above imports so the mock applies before the module loads. For partial mocks, call importOriginal inside the factory and spread the actual exports. Use vi.doMock for non-hoisted dynamic mocking with await import.

Install @vitest/coverage-v8 or @vitest/coverage-istanbul, then set coverage.provider in the test config and run vitest run --coverage. In v4, define coverage.include explicitly to report uncovered files, since coverage.all was removed.

Vitest provides a Jest-compatible API while sharing Vite's config, transformers, and plugins, giving native ESM and TypeScript support without extra setup. Its watch mode reruns only affected tests based on the module graph, which suits Vite-based projects.

Yes, Vitest Browser Mode runs tests in real browsers via providers like Playwright. In v4 the provider is an object such as playwright(), instances specify browsers like chromium, and test context imports from vitest/browser.

Vitest v4 removed poolOptions, the workspace option, and coverage.all, and changed the default pool to forks. Move pool settings to top-level options like maxWorkers, replace vitest.workspace.ts with projects, and set coverage.include explicitly.

Filter by file path or line number as CLI arguments, by test name with -t, or by declared tags with --tagsFilter expressions like "db && !flaky". Use --project to run named projects, and vitest related to run tests importing specific files.