feat(jest): respect transpilePackages in tests

packages/next/build/jest/jest.ts

@@ -95,6 +95,9 @@ export default function nextJest(options: { dir?: string } = {}) {
         await lockfilePatchPromise.cur
       }
 
+      const transpiled = (
+        nextConfig?.experimental?.transpilePackages ?? []
+      ).join('|')
       return {
         ...resolvedJestConfig,
 
@@ -151,8 +154,16 @@ export default function nextJest(options: { dir?: string } = {}) {
         },
 
         transformIgnorePatterns: [
-          // To match Next.js behavior node_modules is not transformed
-          '/node_modules/',
+          // To match Next.js behavior node_modules is not transformed, only `transpiledPackages`
+          ...(transpiled
+            ? [
+                `/node_modules/(?!(${transpiled}))/`,
+                `/node_modules/.pnpm/(?!(${transpiled.replace(
+                  /\//g,
+                  '\\+'
+                )})@)`,
+              ]
+            : ['/node_modules/']),
           // CSS modules are mocked so they don't need to be transformed
           '^.+\\.module\\.(css|sass|scss)$',
 

test/production/jest/transpile-packages.test.ts

@@ -0,0 +1,43 @@
+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': `import capitalize from '@hashicorp/platform-util/text/capitalize'
+        export default function Home() {
+          return capitalize('test')
+        }`,
+        'index.test.ts': `import capitalize from '@hashicorp/platform-util/text/capitalize'
+        it('should work', () => {
+          expect(capitalize('test')).toEqual('Test')
+        })`,
+        'jest.config.js': `module.exports = require('next/jest')({ dir: './' })()`,
+        'next.config.js': `module.exports = {
+          experimental: { transpilePackages: ['@hashicorp/platform-util'] },
+        }`,
+      },
+      packageJson: {
+        scripts: {
+          // Runs jest and bails if jest fails
+          build: 'next build && yarn jest',
+        },
+      },
+      buildCommand: `yarn build`,
+      dependencies: {
+        '@hashicorp/platform-util': '0.2.0',
+        '@types/react': 'latest',
+        jest: '27.4.7',
+      },
+    })
+  })
+  afterAll(() => next.destroy())
+
+  it('should work', async () => {
+    const html = await renderViaHTTP(next.url, '/')
+    expect(html).toContain('Test')
+  })
+})