Vitest
> Blazing fast unit testing powered by Vite — Jest-compatible API, native ESM, TypeScript.
Best use case
Vitest is best used when you need a repeatable AI agent workflow instead of a one-off prompt.
> Blazing fast unit testing powered by Vite — Jest-compatible API, native ESM, TypeScript.
Teams using Vitest should expect a more consistent output, faster repeated execution, less prompt rewriting.
When to use this skill
- You want a reusable workflow that can be run more than once with consistent structure.
When not to use this skill
- You only need a quick one-off answer and do not need a reusable workflow.
- You cannot install or maintain the underlying files, dependencies, or repository context.
Installation
Claude Code / Cursor / Codex
Manual Installation
- Download SKILL.md from GitHub
- Place it in
.claude/skills/vitest/SKILL.mdinside your project - Restart your AI agent — it will auto-discover the skill
How Vitest Compares
| Feature / Agent | Vitest | Standard Approach |
|---|---|---|
| Platform Support | Not specified | Limited / Varies |
| Context Awareness | High | Baseline |
| Installation Complexity | Unknown | N/A |
Frequently Asked Questions
What does this skill do?
> Blazing fast unit testing powered by Vite — Jest-compatible API, native ESM, TypeScript.
Where can I find the source code?
You can find the source code on GitHub using the link provided at the top of the page.
Related Guides
SKILL.md Source
# Vitest
> Blazing fast unit testing powered by Vite — Jest-compatible API, native ESM, TypeScript.
## When to Use
- Unit and integration testing for Vite/React/Vue/Svelte projects
- Replacing Jest with faster, ESM-native alternative
- Component testing with happy-dom or jsdom
- In-source testing (tests alongside implementation)
## Core Patterns
### Configuration
```typescript
// vitest.config.ts
import { defineConfig } from "vitest/config";
import react from "@vitejs/plugin-react";
export default defineConfig({
plugins: [react()],
test: {
globals: true, // No need for import { test, expect }
environment: "happy-dom", // or "jsdom" for browser APIs
setupFiles: ["./test/setup.ts"],
coverage: {
provider: "v8",
reporter: ["text", "html"],
},
include: ["src/**/*.{test,spec}.{ts,tsx}"],
},
});
```
### Testing
```typescript
import { describe, it, expect, vi, beforeEach } from "vitest";
describe("UserService", () => {
beforeEach(() => { vi.clearAllMocks(); });
it("creates user", async () => {
const mockDb = vi.fn().mockResolvedValue({ id: "1", name: "Inu" });
const user = await createUser(mockDb, { name: "Inu" });
expect(user).toMatchObject({ id: "1", name: "Inu" });
expect(mockDb).toHaveBeenCalledOnce();
});
it("throws on invalid input", () => {
expect(() => validateName("")).toThrow("Name required");
});
});
```
### Key Features
- **vi.fn()**: Mock functions (same API as jest.fn())
- **vi.mock()**: Module mocking with auto-mock support
- **vi.spyOn()**: Spy on object methods
- **Snapshots**: `expect(result).toMatchSnapshot()`
- **In-source**: `if (import.meta.vitest)` blocks stripped from production
- **Watch mode**: `vitest` (default), `vitest run` for CI
- **Workspace**: `vitest.workspace.ts` for monorepo testing
- **Type testing**: `expectTypeOf<string>().toMatchTypeOf<string>()`
- **Browser mode**: `vitest --browser` for real browser testingRelated Skills
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