Switch to ESM Jest config in docs

[karlhorky]

Thanks again for Next.js 13! Finding a bunch of new ways to improve things 🙌

Just a quick PR to switch the Jest configuration file with next/jest to ESM to eliminate another instance of CommonJS.

ESM requires a .js extension on the import.

An alternative would be to switch to a TypeScript config file (jest.config.ts) which would (I am guessing) not require this file extension (but still allow switching to an ESM-style import syntax).

New jest.config.mjs file:

import nextJest from 'next/jest.js'

const createJestConfig = nextJest({
  // Provide the path to your Next.js app to load next.config.js and .env files in your test environment
  dir: './',
})

// Add any custom config to be passed to Jest
/** @type {import('jest').Config} */
const config = {
  // Add more setup options before each test is run
  // setupFilesAfterEnv: ['<rootDir>/jest.setup.js'],
  // if using TypeScript with a baseUrl set to the root directory then you need the below for alias' to work
  moduleDirectories: ['node_modules', '<rootDir>/'],
  testEnvironment: 'jest-environment-jsdom',
}

// createJestConfig is exported this way to ensure that next/jest can load the Next.js config which is async
export default createJestConfig(config)

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have a helpful link attached, see contributing.md

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have a helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes by running pnpm build && pnpm lint
• The "examples guidelines" are followed from our contributing doc

[karlhorky]

Thanks for the review and merge!