next.js/test/unit/eslint-plugin-next/no-head-import-in-document.test.ts

import { RuleTester } from 'eslint'
import { rules } from '@next/eslint-plugin-next'

const NextESLintRule = rules['no-head-import-in-document']

const tests = {
  valid: [
    {
      code: `import Document, { Html, Head, Main, NextScript } from 'next/document'

      class MyDocument extends Document {
        static async getInitialProps(ctx) {
          //...
        }

        render() {
          return (
            <Html>
              <Head>
              </Head>
            </Html>
          )
        }
      }

      export default MyDocument
    `,
      filename: 'pages/_document.tsx',
    },
    {
      code: `import Head from "next/head";

      export default function IndexPage() {
        return (
          <Head>
            <title>My page title</title>
            <meta name="viewport" content="initial-scale=1.0, width=device-width" />
          </Head>
        );
      }
    `,
      filename: 'pages/index.tsx',
    },
  ],
  invalid: [
    {
      code: `
      import Document, { Html, Main, NextScript } from 'next/document'
      import Head from 'next/head'

      class MyDocument extends Document {
        render() {
          return (
            <Html>
              <Head />
              <body>
                <Main />
                <NextScript />
              </body>
            </Html>
          )
        }
      }

      export default MyDocument
      `,
      filename: 'pages/_document.js',
      errors: [
        {
          message:
            '`next/head` should not be imported in `pages/_document.js`. Use `<Head />` from `next/document` instead. See: https://nextjs.org/docs/messages/no-head-import-in-document',
          type: 'ImportDeclaration',
        },
      ],
    },
    {
      code: `
      import Document, { Html, Main, NextScript } from 'next/document'
      import Head from 'next/head'

      class MyDocument extends Document {
        render() {
          return (
            <Html>
              <Head />
              <body>
                <Main />
                <NextScript />
              </body>
            </Html>
          )
        }
      }

      export default MyDocument
      `,
      filename: 'pages/_document.page.tsx',
      errors: [
        {
          message:
            '`next/head` should not be imported in `pages/_document.page.tsx`. Use `<Head />` from `next/document` instead. See: https://nextjs.org/docs/messages/no-head-import-in-document',
          type: 'ImportDeclaration',
        },
      ],
    },
    {
      code: `
      import Document, { Html, Main, NextScript } from 'next/document'
      import Head from 'next/head'

      class MyDocument extends Document {
        render() {
          return (
            <Html>
              <Head />
              <body>
                <Main />
                <NextScript />
              </body>
            </Html>
          )
        }
      }

      export default MyDocument
      `,
      filename: 'pages/_document/index.js',
      errors: [
        {
          message:
            '`next/head` should not be imported in `pages/_document/index.js`. Use `<Head />` from `next/document` instead. See: https://nextjs.org/docs/messages/no-head-import-in-document',
          type: 'ImportDeclaration',
        },
      ],
    },
    {
      code: `
      import Document, { Html, Main, NextScript } from 'next/document'
      import Head from 'next/head'

      class MyDocument extends Document {
        render() {
          return (
            <Html>
              <Head />
              <body>
                <Main />
                <NextScript />
              </body>
            </Html>
          )
        }
      }

      export default MyDocument
      `,
      filename: 'pages/_document/index.tsx',
      errors: [
        {
          message:
            '`next/head` should not be imported in `pages/_document/index.tsx`. Use `<Head />` from `next/document` instead. See: https://nextjs.org/docs/messages/no-head-import-in-document',
          type: 'ImportDeclaration',
        },
      ],
    },
  ],
}

describe('no-head-import-in-document', () => {
  new RuleTester({
    languageOptions: {
      ecmaVersion: 2018,
      sourceType: 'module',
      parserOptions: {
        ecmaFeatures: {
          modules: true,
          jsx: true,
        },
      },
    },
  }).run('eslint', NextESLintRule, tests)
})