Vitest

lastmod 2026-09-23created 2022-04-203 edits

Features

• Vite's config, transformers, resolvers, and plugins.
• Use the same setup from your app to run the tests!
• Smart & instant watch mode, like HMR for tests!
• Components testing for Vue, React, Svelte, Lit and more
• Out-of-box TypeScript / JSX support
• ESM first, top level await
• Workers multi-threading via tinypool
• Filtering, timeouts, concurrent for suite and tests
• Jest Snapshot
• Chai built-in for assertions + Jest expect compatible APIs
• Tinyspy built-in for mocking
• happy-dom or jsdom for DOM mocking
• Native code coverage via c8
• Rust like in-source testing

Static imports not available in vi.hoisted

• Vi | Vitest # vi.hoisted

It says "IMPORTS ARE NOT AVAILABLE" in huge letters.

Reducing the number of Vitest workers

One-off: run flags

./npm run test:run -- --maxWorkers=4
./npm run test:run -- --maxWorkers=25%       # 코어 대비 비율
./npm run test:run -- --no-file-parallelism  # 파일을 하나씩 순차 실행

Permanent: config file

In Vitest 4, use maxWorkers directly under test instead of the old poolOptions.threads.maxThreads.

test: {
  maxWorkers: process.env.CI ? undefined : '50%',
  // ...
}

OS-level resource limits

Reliably constrains CPU and memory regardless of Vitest settings.

systemd-run --user --scope -p CPUQuota=400% -p MemoryMax=12G ./npm run test:run
nice -n 19 ./npm run test:run
taskset -c 0-3 ./npm run test:run

Per-worker Node heap limit

NODE_OPTIONS=--max-old-space-size=2048 ./npm run test:run

Note that a worker hitting the limit dies with OOM (out of memory) and the test fails.

See also

• vue
• vite