LLM Best Practices

Jest vs Vitest

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This is LLM Best Practices (llmbestpractices.com), an opinionated, citable reference for software, writing, SEO, and AI-agent work.

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Overview

Use Vitest for any new web, Node, or library project; use Jest for React Native and for large suites that already pass. As of 2026-10-01 Vitest is at 5.0 (released 2026-09-03; needs Vite 6.4+ and Node 22.12+) and Jest is at 30.x. The test APIs are close enough that migration is mostly mechanical.

Comparison

DimensionVitest 5Jest 30
ConfigReuses vite.config.* (aliases, plugins)Separate jest.config.*
ESMNativeExperimental; needs node --experimental-vm-modules
TypeScriptWorks without a transformNeeds @swc/jest, babel-jest, or ts-jest
Browser testsBrowser Mode (stable since Vitest 4): Playwright, WebdriverIO, or preview provider; toMatchScreenshotjsdom or happy-dom only; use Playwright separately
Mock APIvi.fn, vi.mock, vi.spyOnjest.fn, jest.mock, jest.spyOn
React NativeNo official supportDefault runner in the RN template
Monoreposprojects configprojects config

Pick Vitest when

Pick Vitest whenever the project builds with Vite, ships ESM, or is written in TypeScript.

  • One config serves build and test, so path aliases and plugins cannot drift.
  • Use Browser Mode for components that need a real DOM instead of jsdom. See playwright-vs-cypress for end-to-end tests.
  • Vitest 5 sets clearMocks on by default and requires awaited async assertions; fix floating expect(...).resolves calls during the upgrade.

Pick Jest when

Pick Jest when the platform or the existing suite dictates it.

  • React Native and Expo: the template ships with a Jest preset, and Vitest has no official React Native support.
  • A large passing suite on CommonJS: migrating buys little. Replace babel-jest with @swc/jest for speed instead.
  • Third-party tooling that targets Jest’s reporter or runner API, or custom snapshot serializers and matcher packages (such as jest-axe) with no Vitest port.
  • Mixed monorepo: run Vitest in the web packages and Jest in the React Native package; they coexist.

Next.js ships next/jest, which configures the SWC transform for Jest; Vitest works with Next.js through its own setup.

Migrate from Jest to Vitest

Migrate by swapping the runner, then the mock namespace.

  1. Install vitest; move jest.config.* into a test block in vite.config.ts, or use a vitest.config.ts.
  2. Replace jest.* with vi.*. Import vi from vitest, or set globals: true to keep global describe and it.
  3. Drop ts-jest and babel-jest; remove @types/jest if globals are off.
  4. Check fake timers and jest.requireActual equivalents (vi.importActual); these differ most.
  5. Run both runners in CI for one release when the suite is large.

@testing-library/* packages work unchanged. See testing for what to test.

FAQ

Is Vitest easier to set up than Jest for TypeScript?

Yes; Vitest reuses vite.config.*, runs TypeScript without a transform, and handles ESM natively. Jest needs @swc/jest, babel-jest, or ts-jest and treats ESM as experimental.

Can I use Vitest with React Native?

No; Vitest has no official React Native support. Jest is the default runner in the React Native template, so keep Jest there.

How hard is it to migrate from Jest to Vitest?

Mostly mechanical: the test APIs are close, so swap the runner, replace jest.* with vi.*, and drop ts-jest and babel-jest. Fake timers and jest.requireActual (vi.importActual) differ most.

What are the requirements for Vitest 5?

Vitest 5.0 (released 2026-09-03) needs Vite 6.4 or later and Node 22.12 or later. It turns on clearMocks by default and requires awaited async assertions.

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