Vitest

Vitest is a next-generation testing framework powered by Vite. It provides a Jest-compatible API with native ESM, TypeScript, and JSX support out of the box. Vitest shares the same config, transformers, resolvers, and plugins with your Vite app.

Key Features:

• Vite-native: Uses Vite's transformation pipeline for fast HMR-like test updates
• Jest-compatible: Drop-in replacement for most Jest test suites
• Smart watch mode: Only reruns affected tests based on module graph
• Native ESM, TypeScript, JSX support without configuration
• Multi-threaded workers for parallel test execution
• Built-in coverage via V8 or Istanbul
• Snapshot testing, mocking, and spy utilities

The skill is based on Vitest 3.x, generated at 2026-01-28.

Core

Topic	Description	Reference
Configuration	Vitest and Vite config integration, defineConfig usage	core-config
CLI	Command line interface, commands and options	core-cli
Test API	test/it function, modifiers like skip, only, concurrent	core-test-api
Describe API	describe/suite for grouping tests and nested suites	core-describe
Expect API	Assertions with toBe, toEqual, matchers and asymmetric matchers	core-expect
Hooks	beforeEach, afterEach, beforeAll, afterAll, aroundEach	core-hooks

Features

Topic	Description	Reference
Mocking	Mock functions, modules, timers, dates with vi utilities	features-mocking
Snapshots	Snapshot testing with toMatchSnapshot and inline snapshots	features-snapshots
Coverage	Code coverage with V8 or Istanbul providers	features-coverage
Test Context	Test fixtures, context.expect, test.extend for custom fixtures	features-context
Concurrency	Concurrent tests, parallel execution, sharding	features-concurrency
Filtering	Filter tests by name, file patterns, tags	features-filtering

Advanced

Topic	Description	Reference
Vi Utilities	vi helper: mock, spyOn, fake timers, hoisted, waitFor	advanced-vi
Environments	Test environments: node, jsdom, happy-dom, custom	advanced-environments
Type Testing	Type-level testing with expectTypeOf and assertType	advanced-type-testing
Projects	Multi-project workspaces, different configs per project	advanced-projects