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vitest

Vitest fast unit testing framework powered by Vite with Jest-compatible API. Use when writing tests, mocking, configuring coverage, or working with test filtering and fixtures.

Published by antfu ↗antfu/skills

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vitest

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Use vitest to add or improve unit tests for [target behavior], including appropriate mocks, fixtures, or coverage configuration where needed.

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  • [target behavior]

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SKILL.md

name: vitestdescription: Vitest fast unit testing framework powered by Vite with Jest-compatible API. Use when writing tests, mocking, configuring coverage, or working with test filtering and fixtures.metadata:   author: Anthony Fu  version: "2026.10.23"  source: Generated from https://github.com/vitest-dev/vitest, scripts located at https://github.com/antfu/skills

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 5.1.0-beta.1, generated at 2026-10-23.

Core

TopicDescriptionReference
ConfigurationVitest and Vite config integration, defineConfig usagecore-config
CLICommand line interface, commands and optionscore-cli
Test APItest/it function, modifiers like skip, only, concurrentcore-test-api
Describe APIdescribe/suite for grouping tests and nested suitescore-describe
Expect APIAssertions with toBe, toEqual, matchers and asymmetric matcherscore-expect
HooksbeforeEach, afterEach, beforeAll, afterAll, aroundEachcore-hooks

Features

TopicDescriptionReference
MockingMock functions, modules, timers, dates with vi utilitiesfeatures-mocking
SnapshotsSnapshot testing with toMatchSnapshot and inline snapshotsfeatures-snapshots
CoverageCode coverage with V8 or Istanbul providersfeatures-coverage
Test ContextTest fixtures, context.expect, test.extend for custom fixturesfeatures-context
ConcurrencyConcurrent tests, parallel execution, shardingfeatures-concurrency
FilteringFilter tests by name, file patterns, tagsfeatures-filtering
Test TagsLabel tests with tags to filter runs and apply shared optionsfeatures-test-tags
ReportersBuilt-in reporters, default selection, CI/output configfeatures-reporters
BenchmarkingWrite benchmarks with the bench fixture (Tinybench)features-benchmarking

Advanced

TopicDescriptionReference
Vi Utilitiesvi helper: mock, spyOn, fake timers, hoisted, waitForadvanced-vi
EnvironmentsTest environments: node, jsdom, happy-dom, customadvanced-environments
Type TestingType-level testing with expectTypeOf and assertTypeadvanced-type-testing
ProjectsMulti-project workspaces, different configs per projectadvanced-projects