This PR updates the testing guides to use App Router and TypeScript,
also updates `/examples` to show `app` and `pages` examples.
## Overview
- [x] Create a new "Testing" section that is shared between `app` and
`pages`.
- [x] Explain the differences between E2E, unit testing, component
testing, etc.
- [x] Recommend E2E for `async` components as currently none of the
tools support it.
- [x] Update setup guides for **Cypress**, **Playwright**, and **Jest**
with latest config options, and examples for `app` and `pages`.
- [x] Add new guide for **Vitest**
- [x] Clean up `/examples`: use TS, show `app` and `pages` examples,
match docs config
## Cypress
- [x] E2E Tests
- [x] Component Testing
- [x] Client Components
- [x] Server Components
- [ ] `async` components
**Blockers:**
- TS: `Option 'bundler' can only be used when 'module' is set to
'es2015' or later`. In **tsconfig.json** compilerOptions, Next.js uses
"moduleResolution": "bundler", changing it to "node" fixes the issue but
it can have repercussions.
- https://github.com/cypress-io/cypress/issues/27731
- Version 14 is currently not supported for component testing
- https://github.com/cypress-io/cypress/issues/28185
## Playwright
- [x] E2E Tests
## Jest
- [x] Unit Testing
- [x] Client Components
- [x] Server Components
- [ ] `async` components:
https://github.com/testing-library/react-testing-library/issues/1209
- [x] 'server-only': https://github.com/vercel/next.js/pull/54891
- [x] Snapshot Testing
**Blockers:**
- TS: https://github.com/testing-library/jest-dom/issues/546
- None of the solutions in the issue work with Next.js v14.0.4 and TS v5
## Vitest
- [x] Unit Testing
- [x] Client Components
- [x] Server Components
- [ ] `async` components
- [x] 'server-only'
- [x] Update vitest example
- [x] Handles CSS, and CSS modules imports
- [x] Handles next/image
## Other
- https://github.com/vercel/next.js/issues/47448
- https://github.com/vercel/next.js/issues/47299
