Ensure mjs files are transformed with jest

packages/next/build/jest/jest.ts

@@ -100,7 +100,7 @@ export default function nextJest(options: { dir?: string } = {}) {
 
         transform: {
           // Use SWC to compile tests
-          '^.+\\.(js|jsx|ts|tsx)$': [
+          '^.+\\.(js|jsx|ts|tsx|mjs)$': [
             require.resolve('../swc/jest-transformer'),
             {
               nextConfig,

packages/next/build/swc/jest-transformer.js

@@ -37,10 +37,6 @@ const isSupportEsm = 'Module' in vm
 module.exports = {
   createTransformer: (inputOptions) => ({
     process(src, filename, jestOptions) {
-      if (!/\.[jt]sx?$/.test(filename)) {
-        return src
-      }
-
       const jestConfig = getJestConfig(jestOptions)
 
       let swcTransformOpts = getJestSWCOptions({

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

@@ -80,6 +80,21 @@ describe('next/jest', () => {
             });
           });
         `,
+        'lib/hello.mjs': `
+          import path from 'path'
+
+          export default function hello() {
+            return path.join('hello', 'world')
+          }
+        `,
+        'test/mjs-support.test.js': `
+          import path from 'path'
+          import hello from '../lib/hello.mjs'
+
+          it('should transpile .mjs file correctly', async () => {
+            expect(hello()).toBe(path.join('hello', 'world'))
+          })
+        `,
         'test/mock.test.js': `
           import router from 'next/router'
 

test/unit/jest-next-swc.test.ts

@@ -1,5 +1,4 @@
 /* eslint-env jest */
-
 describe('jest next-swc preset', () => {
   it('should have correct env', async () => {
     expect(process.env.NODE_ENV).toBe('test')