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.

Vitest provides a Jest-compatible API, so most test files work by replacing jest imports with vitest equivalents like vi.fn and vi.spyOn. Update your config to vitest.config.ts and adjust coverage settings, since v4 removed coverage.all and requires explicit coverage.include.

Yes, Vitest supports jsdom and happy-dom environments configured via the environment option or a per-file @vitest-environment comment. For real browser testing, use Vitest Browser Mode with the Playwright provider instead.

Filter by file path as a CLI argument, by test name with -t or --testNamePattern, or by declared tags with --tagsFilter. You can also use test.only in development, vitest --changed for modified files, and vitest related for tests importing specific files.

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 test.projects, and define coverage.include explicitly.

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.