Vitest

# Vitest Setup

Detect the project type, generate the right Vitest configuration, and produce working test infrastructure. Not a reference card — this skill creates files.

## Workflow

1. **Detect** — scan the project to determine type and existing setup
2. **Configure** — generate vitest.config.ts tailored to the environment
3. **Scaffold** — create test setup, utilities, and a sample test
4. **Wire up** — add package.json scripts and TypeScript config

## Step 1: Detect Project Type

Read these files to determine the project:

```
package.json          → dependencies, scripts, type field
tsconfig.json         → paths, compiler options
wrangler.toml         → Cloudflare Workers project
vite.config.ts        → existing Vite setup (extend, don't replace)
vitest.config.ts      → already configured? just fill gaps
jest.config.*         → migration candidate
src/                  → source structure
```

Classify as one of:

| Type | Signals | Environment |
|------|---------|-------------|
| **Cloudflare Workers** | wrangler.toml, @cloudflare/workers-types, cloudflare vite plugin | `node` with Workers-specific setup |
| **React (Vite)** | @vitejs/plugin-react, react-dom | `jsdom` or `happy-dom` |
| **React (SSR/TanStack Start)** | @tanstack/start, vinxi | Split: `node` for server, `jsdom` for client |
| **Node/Hono API** | hono, express, no react-dom | `node` |
| **Library** | exports field, no framework deps | `node` |

If a `vite.config.ts` already exists, extend it rather than creating a separate vitest.config.ts — Vitest reads Vite config natively.

## Step 2: Install Dependencies

Generate the install command based on detected type:

```bash
# Base (always)
pnpm add -D vitest

# React projects — add jsdom and Testing Library
pnpm add -D @vitest/coverage-v8 jsdom @testing-library/react @testing-library/jest-dom @testing-library/user-event

# Workers projects — add Cloudflare test utilities
pnpm add -D @vitest/coverage-v8 @cloudflare/vitest-pool-workers

# Node/Hono projects
pnpm add -D @vitest/coverage-v8

# If migrating from Jest, also remove:
pnpm remove jest ts-jest @types/jest jest-environment-jsdom babel-jest
```

Use the project's package manager (check for pnpm-lock.yaml, yarn.lock, bun.lockb, or package-lock.json).

## Step 3: Generate vitest.config.ts

### Cloudflare Workers

```typescript
import { defineWorkersConfig } from "@cloudflare/vitest-pool-workers/config";

export default defineWorkersConfig({
  test: {
    globals: true,
    poolOptions: {
      workers: {
        wrangler: { configPath: "./wrangler.toml" },
      },
    },
  },
});
```

If the project uses the Cloudflare Vite plugin (`@cloudflare/vite-plugin`), integrate into the existing vite.config.ts instead:

```typescript
/// <reference types="vitest/config" />
import { defineConfig } from "vite";
import { cloudflare } from "@cloudflare/vite-plugin";

export default defineConfig({
  plugins: [cloudflare()],
  test: {
    globals: true,
  },
});
```

### React (Vite)

```typescript
/// <reference types="vitest/config" />
import { defineConfig } from "vite";
import react from "@vitejs/plugin-react";

export default defineConfig({
  plugins: [react()],
  test: {
    globals: true,
    environment: "jsdom",
    setupFiles: ["./src/test/setup.ts"],
    css: true,
  },
});
```

If a vite.config.ts already exists, add the `test` block to it rather than creating a new file.

### Node / Hono API

```typescript
import { defineConfig } from "vitest/config";

export default defineConfig({
  test: {
    globals: true