vitest

Use vi.mock with a factory function, which is hoisted to the top of the file before imports run. For partial mocks, call importOriginal inside the factory and spread the actual module. Use vi.doMock for non-hoisted dynamic mocking with await import.

Install @vitest/coverage-v8 and run vitest run --coverage, or set coverage.enabled to true in vitest.config.ts. V8 is the default faster provider; Istanbul offers broader compatibility. Configure reporters, include patterns, and thresholds under the coverage key.

Yes, set environment to 'jsdom' in your config or add a // @vitest-environment jsdom comment at the top of a test file. happy-dom is a faster alternative with fewer APIs. Install jsdom or happy-dom as a dev dependency first.

Vitest provides a Jest-compatible API, so most test suites work as drop-in replacements using the same describe, test, and expect functions. It adds native ESM and TypeScript support and shares your Vite config, transformers, and plugins.

vi.mock calls are hoisted above imports, so they cannot reference variables declared later in the file. Wrap shared mock values in vi.hoisted so they are defined before the mock factory executes.

Use vitest -t "pattern" to filter by test name, pass a file path or filename substring as a positional argument, or add test.only to focus a single test. The --changed flag runs tests affected by uncommitted changes, and --tags filters by custom tags.