vitest

Add a test property to vite.config.ts with a Vitest types reference, or create a separate vitest.config.ts which takes priority. Use mergeConfig from vitest/config to combine separate config files when needed.

Use vi.mock for hoisted module mocking, vi.fn for mock functions, and vi.spyOn to track existing methods. For dynamic imports use vi.doMock, and use vi.hoisted to reference variables inside mock factories.

Vitest provides a Jest-compatible API, so most suites migrate by swapping imports to vitest and adjusting configuration. Watch for v4/v5 changes like the forks pool default, removed poolOptions, and removed test.sequential.

Yes, Vitest supports jsdom and happy-dom environments configured globally or per file with the @vitest-environment comment. For real browser testing, use Vitest Browser Mode with providers like Playwright.

Since v4, coverage.all was removed, so only files loaded during the run are reported by default. Set coverage.include explicitly, for example src/**/*.ts, to report uncovered source files too.

Use the --shard=index/count flag on each machine with the blob reporter, then run vitest --merge-reports to combine results into a final junit or json report. Coverage can also be merged this way.