vitest

antfu/skills · Agent Skill

Vitest testing best practices for unit tests, mocking, coverage, fixtures, and test filtering.

Overview

Publisher	antfuCommunity
Repository	antfu/skills ↗
Skill folder	`vitest`
Stars	6,011
Forks	338
Bundled files	21
License	MIT
Last updated	October 23, 2026
Links	Skill source ↗ · Repository ↗

Mozgi check

What we found in the skill files. Details come with a subscription.

Security

low risk · no obvious risks found — the full report shows the details

Compatibility

instructions only — works with most agents

Similar skills

62 similar skills found

Also with subscription

Installation

A skill is a folder with a SKILL.md file. Pick your agent and run the commands in a terminal (macOS, Linux or Git Bash on Windows) from your project root.

Copy the prompt into Claude, Codex or another assistant: it will review the skill and install it for you.

Install the “vitest” skill from mozgi.io (https://mozgi.io/skills/antfu-vitest/) for me.

1. Download the archive: https://mozgi.io/skills/antfu-vitest/download
   If it fails, take the skill folder from the source: https://github.com/antfu/skills/tree/main/skills/vitest
2. Read SKILL.md and the other files. Check the skill is safe: no hidden commands, no sending data elsewhere, no scripts doing something other than described. If anything looks suspicious, stop and tell me.
3. Put the “vitest” folder into your agent's skills folder: .claude/skills/ for Claude Code, .agents/skills/ for Codex, .cursor/skills/ for Cursor, .gemini/skills/ for Gemini CLI. Inside the project if we are in one, otherwise in the home folder (~/.claude/skills/ etc.).
4. Make sure <skills folder>/vitest/SKILL.md exists.
5. Briefly tell me what this skill does and offer to try it on my task.

If you cannot do a step yourself, tell me what to click or type.

git clone --depth 1 --branch main https://github.com/antfu/skills.git /tmp/skills
mkdir -p .claude/skills
cp -r /tmp/skills/skills/vitest .claude/skills/vitest

Restart Claude Code — the skill appears in the list; call it manually with /vitest. For all projects use ~/.claude/skills.

git clone --depth 1 --branch main https://github.com/antfu/skills.git /tmp/skills
mkdir -p .agents/skills
cp -r /tmp/skills/skills/vitest .agents/skills/vitest

Codex looks for skills in .agents/skills from the current folder up to the repo root; call one with /skills or $vitest. For all projects use ~/.agents/skills.

git clone --depth 1 --branch main https://github.com/antfu/skills.git /tmp/skills
mkdir -p .cursor/skills
cp -r /tmp/skills/skills/vitest .cursor/skills/vitest

Cursor picks the skill up on start; call it with “/” in Agent chat. Cursor also reads .claude/skills and .agents/skills. For all projects use ~/.cursor/skills.

git clone --depth 1 --branch main https://github.com/antfu/skills.git /tmp/skills
mkdir -p .gemini/skills
cp -r /tmp/skills/skills/vitest .gemini/skills/vitest

Gemini CLI offers to activate the skill when a task matches — you approve it. For all projects use ~/.gemini/skills.

Review the source files

21 files Download Zip

Read SKILL.md and any companion files before deciding whether to install. Click a file to preview it.

SKILL.md contents

Original author text · read-only

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

| 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 ↗ |

| Test Tags | Label tests with tags to filter runs and apply shared options | features-test-tags ↗ |

| Reporters | Built-in reporters, default selection, CI/output config | features-reporters ↗ |

| Benchmarking | Write benchmarks with the bench fixture (Tinybench) | features-benchmarking ↗ |

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 ↗ |

Frequently asked questions

What does the vitest skill do?

Vitest testing best practices for unit tests, mocking, coverage, fixtures, and test filtering.

How do I install vitest?

Open the “Installation” block on this page and pick your agent — Claude Code, Codex, Cursor or Gemini CLI — for ready-made commands that copy the skill folder to the right place. Or copy the prompt from the “Via assistant” tab and let the assistant review and install the skill.

Which AI models work with vitest?

Skills are plain Markdown instructions (the Agent Skills format), so vitest works with any agent that reads SKILL.md: Claude Code, Codex, Cursor, Gemini CLI, GitHub Copilot, OpenCode and more. The model loads the instructions only when a task matches the skill's description.

Is vitest free?

The skill is published openly by antfu under the MIT license. The skill itself costs nothing — you only pay your AI provider for the tokens you use.

Is it safe to install skills?

A skill is a set of instructions your agent will follow, so read SKILL.md and its companion files before installing. Scripts in the skill folder only run if your agent runs them — keep an eye on what it does and do not grant unnecessary permissions.

How is a skill different from an MCP server or a plugin?

An MCP server or plugin gives the model new tools — code that runs and returns a result. A skill gives it knowledge and process: how to approach a task, which steps to follow and what good output looks like. It needs no server or API key.

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