vitest

The full skill.

Original instructions from the publisher’s SKILL.md

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)         |