Enable jest hoist transform when using next/jest

packages/next/build/swc/options.js

@@ -38,6 +38,14 @@ export function getBaseSWCOptions({
       },
 
       transform: {
+        // Enables https://github.com/swc-project/swc/blob/0359deb4841be743d73db4536d4a22ac797d7f65/crates/swc_ecma_ext_transforms/src/jest.rs
+        ...(jest
+          ? {
+              hidden: {
+                jest: true,
+              },
+            }
+          : {}),
         legacyDecorator: enableDecorators,
         react: {
           importSource: jsConfig?.compilerOptions?.jsxImportSource || 'react',

test/lib/create-next-install.js

@@ -6,7 +6,11 @@ const childProcess = require('child_process')
 const { linkPackages } =
   require('../../.github/actions/next-stats-action/src/prepare/repo-setup')()
 
-async function createNextInstall(dependencies, installCommand) {
+async function createNextInstall(
+  dependencies,
+  installCommand,
+  packageJson = {}
+) {
   const tmpDir = await fs.realpath(process.env.NEXT_TEST_DIR || os.tmpdir())
   const origRepoDir = path.join(__dirname, '../../')
   const installDir = path.join(tmpDir, `next-install-${Date.now()}`)
@@ -56,6 +60,7 @@ async function createNextInstall(dependencies, installCommand) {
     path.join(installDir, 'package.json'),
     JSON.stringify(
       {
+        ...packageJson,
         dependencies: combinedDependencies,
         private: true,
       },

test/lib/e2e-utils.ts

@@ -1,7 +1,7 @@
 import path from 'path'
 import assert from 'assert'
 import { NextConfig } from 'next'
-import { InstallCommand, NextInstance } from './next-modes/base'
+import { InstallCommand, NextInstance, PackageJson } from './next-modes/base'
 import { NextDevInstance } from './next-modes/next-dev'
 import { NextStartInstance } from './next-modes/next-start'
 
@@ -113,6 +113,7 @@ export async function createNext(opts: {
   skipStart?: boolean
   installCommand?: InstallCommand
   buildCommand?: string
+  packageJson?: PackageJson
   startCommand?: string
 }): Promise<NextInstance> {
   try {

test/lib/next-modes/base.ts

@@ -12,6 +12,9 @@ export type InstallCommand =
   | string
   | ((ctx: { dependencies: { [key: string]: string } }) => string)
 
+export type PackageJson = {
+  [key: string]: unknown
+}
 export class NextInstance {
   protected files: {
     [filename: string]: string | FileRef
@@ -28,6 +31,7 @@ export class NextInstance {
   protected childProcess: ChildProcess
   protected _url: string
   protected _parsedUrl: URL
+  protected packageJson: PackageJson
 
   constructor({
     files,
@@ -36,13 +40,15 @@ export class NextInstance {
     installCommand,
     buildCommand,
     startCommand,
+    packageJson = {},
   }: {
     files: {
       [filename: string]: string | FileRef
     }
     dependencies?: {
       [name: string]: string
     }
+    packageJson?: PackageJson
     nextConfig?: NextConfig
     installCommand?: InstallCommand
     buildCommand?: string
@@ -54,6 +60,7 @@ export class NextInstance {
     this.installCommand = installCommand
     this.buildCommand = buildCommand
     this.startCommand = startCommand
+    this.packageJson = packageJson
     this.events = {}
     this.isDestroyed = false
     this.isStopping = false
@@ -86,8 +93,10 @@ export class NextInstance {
           react: 'latest',
           'react-dom': 'latest',
           ...this.dependencies,
+          ...((this.packageJson.dependencies as object | undefined) || {}),
         },
-        this.installCommand
+        this.installCommand,
+        this.packageJson
       )
     }
     console.log('created next.js install, writing test files')

test/production/next/jest/index.test.ts

@@ -0,0 +1,74 @@
+import { createNext } from 'e2e-utils'
+import { NextInstance } from 'test/lib/next-modes/base'
+import { renderViaHTTP } from 'next-test-utils'
+
+describe('next/jest', () => {
+  let next: NextInstance
+
+  beforeAll(async () => {
+    next = await createNext({
+      files: {
+        'pages/index.js': `
+          export default function Page() { 
+            return <p>hello world</p>
+          } 
+        `,
+        'jest.config.js': `
+          // jest.config.js
+          const nextJest = require('next/jest')
+
+          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
+          const customJestConfig = {
+            // 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
+          module.exports = createJestConfig(customJestConfig)
+        `,
+        'test/mock.test.js': `
+          import router from 'next/router'
+
+          jest.mock('next/router', () => ({
+            push: jest.fn(),
+            back: jest.fn(),
+            events: {
+              on: jest.fn(),
+              off: jest.fn(),
+            },
+            asPath: jest.fn().mockReturnThis(),
+            beforePopState: jest.fn(() => null),
+            useRouter: () => ({
+              push: jest.fn(),
+            }),
+          }))
+
+          it('call mocked', async () => {
+            expect(router.push._isMockFunction).toBeTruthy()
+          })
+        `,
+      },
+      dependencies: {
+        jest: '27.4.7',
+      },
+      packageJson: {
+        scripts: {
+          build: 'next build && yarn jest test/mock.test.js',
+        },
+      },
+      buildCommand: `yarn build`,
+    })
+  })
+  afterAll(() => next.destroy())
+
+  it('should work', async () => {
+    const html = await renderViaHTTP(next.url, '/')
+    expect(html).toContain('hello world')
+  })
+})

yarn.lock

@@ -20572,8 +20572,7 @@ webpack-bundle-analyzer@4.3.0:
     source-list-map "^2.0.0"
     source-map "~0.6.1"
 
-"webpack-sources3@npm:webpack-sources@3.2.3", webpack-sources@^3.2.3:
-  name webpack-sources3
+"webpack-sources3@npm:webpack-sources@3.2.3", webpack-sources@^3.2.2, webpack-sources@^3.2.3:
   version "3.2.3"
   resolved "https://registry.yarnpkg.com/webpack-sources/-/webpack-sources-3.2.3.tgz#2d4daab8451fd4b240cc27055ff6a0c2ccea0cde"
   integrity sha512-/DyMEOrDgLKKIG0fmvtz+4dUX/3Ghozwgm6iPp8KRhvn+eQf9+Q7GWxVNMk3+uCPWfdXYC4ExGBckIXdFEfH1w==