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