vitest

Use vi.mock with a factory function, which is hoisted above imports so the mock applies before the module loads. For partial mocks, spread the result of importOriginal and override specific exports; use vi.doMock for non-hoisted dynamic mocking.

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

v4 removed poolOptions (use top-level maxWorkers), removed workspace in favor of projects, and made forks the default pool. v5 removed test.sequential and describe.sequential (use { concurrent: false }) and moved bench to a test-context fixture.

Yes, Vitest supports type testing through expectTypeOf and assertType in .test-d.ts files. Enable it with typecheck.enabled in config and run it with vitest typecheck or the --typecheck flag.

Use the --shard flag with index and count, such as vitest run --shard=1/3, on each machine with the blob reporter. Then merge results with vitest --merge-reports to produce a unified report including coverage.

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