vitest

Add a test property to your vite.config.ts with a /// <reference types="vitest/config" /> directive, or create a separate vitest.config.ts which takes priority. Use mergeConfig from vitest/config to combine separate config files.

Use vi.mock with a factory function, which is hoisted above imports. For partial mocks, spread the result of importOriginal; use { spy: true } to keep real implementations while tracking calls, and vi.doMock for non-hoisted dynamic mocking.

Vitest provides a Jest-compatible API covering test, describe, expect, and mocking, so most suites migrate with minimal changes. It adds native ESM and TypeScript support and shares your Vite config, transformers, and plugins.

Yes, Vitest supports coverage via the V8 provider (default, faster) or Istanbul (more compatible), enabled with the --coverage flag or coverage.enabled config. In v4 you must set coverage.include to report uncovered files, since coverage.all was removed.

Vitest v4 removed poolOptions (use top-level maxWorkers), the workspace option (use projects), and coverage.all; v5 removed test.sequential and describe.sequential (use { concurrent: false }) and made bench a test-context fixture instead of a top-level import.

Set test.environment to jsdom or happy-dom in your config, or add a // @vitest-environment jsdom comment at the top of a file. For real browser testing, use Vitest Browser Mode with the Playwright provider.