test-tslisted

# TypeScript/React testing This project uses **Vitest** as the test runner. The Next.js 16 official documentation recommends Vitest over Jest for App Router projects: native ESM and TypeScript support require no additional transformation configuration, and Vitest runs 3–5x faster than Jest on equivalent suites. Do not introduce Jest. ## Test runner commands ```bash npm test # run all tests once npm run test:watch # watch mode npm run test:coverage # with coverage report # Targeted runs npx vitest run src/components/invoice/ # run tests in a directory npx vitest run -t "renders the client" # filter by test name pattern npx vitest run path/to/component.test.tsx # run a single file ``` ## Decision framework Before writing any test, classify it: | Category | What it covers | Vitest environment | |---|---|---| | **Unit** | Pure functions, utilities, Zod schemas, computed logic | `node` | | **Component** | Client Components rendered with RTL | `jsdom` | | **Hook** | Custom hooks via `renderHook` | `jsdom` | | **Server Action** | `'use server'` functions with mocked Prisma | `node` | | **Integration** | Real database or external service | `node` + env gate | `jsdom` is the default environment configured in `vitest.config.ts`. For Server Actions and utilities, add a file-level directive to switch to `node`: ```typescript // @vitest-environment node import { describe, it, expect, vi, befor