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 5.x (beta), generated at 2026-06-22.

Core

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

Features

Topic	Description	Reference
Mocking	Mock functions, modules, timers, dates with vi utilities	features-mocking [blocked]
Snapshots	Snapshot testing with toMatchSnapshot and inline snapshots	features-snapshots [blocked]
Coverage	Code coverage with V8 or Istanbul providers	features-coverage [blocked]
Test Context	Test fixtures, context.expect, test.extend for custom fixtures	features-context [blocked]
Concurrency	Concurrent tests, parallel execution, sharding	features-concurrency [blocked]
Filtering	Filter tests by name, file patterns, tags	features-filtering [blocked]
Test Tags	Label tests with tags to filter runs and apply shared options	features-test-tags [blocked]
Reporters	Built-in reporters, default selection, CI/output config	features-reporters [blocked]
Benchmarking	Write benchmarks with the bench fixture (Tinybench)	features-benchmarking [blocked]

Advanced

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