vitest

Use when working with Vitest for unit testing, component testing, snapshot testing, or mocking in Vite-based projects. Also use when migrating from Jest to Vitest, configuring Vitest workspaces, or using Vitest Browser Mode for component tests.

Model	Source	Category
sonnet	core	Testing

Full Reference

Vitest

Vitest v4.0.18 · Vite-native · ESM-first · Jest-compatible API

Item	Value
Install	npm install -D vitest
Requires	Vite >= 6.0.0, Node >= 20.0.0
Run	npx vitest (watch) · npx vitest run (once)
Coverage	npx vitest --coverage
UI	npx vitest --ui

Reference Index

Load the file that matches your task:

Task	File
Install, config, environments	reference/setup-and-config.md
describe/it/test, lifecycle hooks, parameterized tests	reference/writing-tests.md
expect matchers, custom matchers, soft assertions	reference/assertions.md
vi.fn, vi.mock, vi.spyOn, module mocking	reference/mocking.md
toMatchSnapshot, inline snapshots, serializers	reference/snapshots.md
Fake timers, setSystemTime, async timers	reference/timers-and-dates.md
React/Vue component testing, Testing Library setup	reference/component-testing.md
Real browser testing, visual regression, traces	reference/browser-mode.md
v8/istanbul providers, thresholds, ignore comments	reference/coverage.md
projects config, monorepo, shared config	reference/monorepo-and-projects.md
TypeScript support, typed mocks, test.extend fixtures	reference/typescript.md
Watch mode, —changed, line filtering, UI mode	reference/watch-and-filtering.md
GitHub Actions, reporters, pool config	reference/ci-and-reporters.md
Migrating from Jest, API mapping, behavioral diffs	reference/jest-migration.md
v4.0 / v3.x breaking changes and new APIs	reference/changelog.md

Common Mistakes

Mistake	Fix
Using jest.fn() instead of vi.fn()	Import vi from vitest — all Jest globals map to vi.*
mockReset() expected to return undefined	Vitest mockReset() restores the original implementation, not an empty function
Using workspace config option	Removed in v4.0 — use projects in vitest.config.ts
Missing coverage.include pattern	v4.0 requires explicit coverage.include for complete reports
String browser provider (provider: 'playwright')	v4.0 requires factory: import { playwright } from '@vitest/browser-playwright'
Importing from @vitest/browser/context	v4.0 moved to vitest/browser
Using poolOptions or maxThreads/maxForks	v4.0: use top-level maxWorkers instead