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](references/core-config.md) | | CLI | Command line interface, commands and options | [core-cli](references/core-cli.md) | | Test API | test/it function, modifiers like skip, only, concurrent | [core-test-api](references/core-test-api.md) | | Describe API | describe/suite for grouping tests and nested suites | [core-describe](references/core-describe.md) | | Expect API | Assertions with toBe, toEqual, matchers and asymmetric matchers | [core-expect](references/core-expect.md) | | Hooks | beforeEach, afterEach, beforeAll, afterAll, aroundEach | [core-hooks](references/core-hooks.md) | ## Features | Topic | Description | Reference | |-------|-------------|-----------| | Mocking | Mock functions, modules, timers, dates with vi utilities | [features-mocking](references/features-mocking.md) | | Snapshots | Snapshot testing with toMatchSnapshot and inline snapshots | [features-snapshots](references/features-snapshots.md) | | Coverage | Code coverage with V8 or Istanbul providers | [features-coverage](references/features-coverage.md) | | Test Context | Test fixtures, context.expect, test.extend for custom fixtures | [features-context](references/features-context.md) | | Concurrency | Concurrent tests, parallel execution, sharding | [features-concurrency](references/features-concurrency.md) | | Filtering | Filter tests by name, file patterns, tags | [features-filtering](references/features-filtering.md) | ## Advanced | Topic | Description | Reference | |-------|-------------|-----------| | Vi Utilities | vi helper: mock, spyOn, fake timers, hoisted, waitFor | [advanced-vi](references/advanced-vi.md) | | Environments | Test environments: node, jsdom, happy-dom, custom | [advanced-environments](references/advanced-environments.md) | | Type Testing | Type-level testing with expectTypeOf and assertType | [advanced-type-testing](references/advanced-type-testing.md) | | Projects | Multi-project workspaces, different configs per project | [advanced-projects](references/advanced-projects.md) |