vitest

Use vi.mock with a factory function, which is hoisted to the top of the file before imports run. For partial mocks, spread the result of importOriginal and override specific exports; use vi.doMock for non-hoisted dynamic mocking with await import.

Install @vitest/coverage-v8 or @vitest/coverage-istanbul, then run vitest with the --coverage flag or set coverage.enabled in the config. Configure reporters, include/exclude patterns, and thresholds under the test.coverage option.

Vitest provides a Jest-compatible API, so most test suites using describe, it, expect, and jest.mock-style patterns work as drop-in replacements. Mocks use the vi helper instead of jest, and configuration moves into vitest.config.ts or vite.config.ts.

Yes, set the environment option to jsdom or happy-dom in the config, or add a // @vitest-environment comment per file. jsdom offers fuller browser API simulation while happy-dom runs faster with fewer APIs.

Synchronous advanceTimersByTime does not await promise callbacks inside timers. Use await vi.advanceTimersByTimeAsync or vi.runAllTimersAsync so microtasks scheduled by timer callbacks resolve before assertions run.

Pass a filename pattern as a CLI argument, use -t or --testNamePattern for test names, or add test.only in the file. You can also filter by tags with --tags, by changed files with --changed, or list matches without running via vitest list.