fix(testing): handle existing jest preset file correctly

packages/jest/preset.ts

@@ -0,0 +1,5 @@
+import { nxPreset } from './preset/jest-preset';
+
+export { nxPreset };
+
+export default nxPreset;

packages/jest/src/generators/configuration/configuration.spec.ts

@@ -262,19 +262,33 @@ describe('jestProject', () => {
     expect(tree.exists('libs/lib1/jest.config.js')).toBeTruthy();
   });
 
-  it('should always use jest.preset.js with --js', async () => {
-    tree.write('jest.preset.ts', '');
+  it('should generate a jest.preset.js when it does not exist', async () => {
     await configurationGenerator(tree, {
       ...defaultOptions,
       project: 'lib1',
       js: true,
     } as JestProjectSchema);
     expect(tree.exists('libs/lib1/jest.config.js')).toBeTruthy();
+    expect(tree.exists('jest.preset.js')).toBeTruthy();
     expect(tree.read('libs/lib1/jest.config.js', 'utf-8')).toContain(
       "preset: '../../jest.preset.js',"
     );
   });
 
+  it('should not override existing jest preset file and should point to it in jest.config files', async () => {
+    tree.write('jest.preset.mjs', 'export default {}');
+    await configurationGenerator(tree, {
+      ...defaultOptions,
+      project: 'lib1',
+      js: true,
+    } as JestProjectSchema);
+    expect(tree.exists('libs/lib1/jest.config.js')).toBeTruthy();
+    expect(tree.exists('jest.preset.mjs')).toBeTruthy();
+    expect(tree.read('libs/lib1/jest.config.js', 'utf-8')).toContain(
+      "preset: '../../jest.preset.mjs',"
+    );
+  });
+
   it('should use module.exports with --js flag', async () => {
     await configurationGenerator(tree, {
       ...defaultOptions,

packages/jest/src/generators/configuration/configuration.ts

@@ -17,7 +17,7 @@ import {
 } from '@nx/devkit';
 import { initGenerator as jsInitGenerator } from '@nx/js';
 import { JestPluginOptions } from '../../plugins/plugin';
-import { isPresetCjs } from '../../utils/config/is-preset-cjs';
+import { getPresetExt } from '../../utils/config/config-file';
 
 const schemaDefaults = {
   setupFile: 'none',
@@ -90,7 +90,7 @@ export async function configurationGeneratorInternal(
     tasks.push(ensureDependencies(tree, options));
   }
 
-  const presetExt = isPresetCjs(tree) ? 'cjs' : 'js';
+  const presetExt = getPresetExt(tree);
 
   await createJestConfig(tree, options, presetExt);
   checkForTestTarget(tree, options);

packages/jest/src/generators/configuration/lib/__snapshots__/create-jest-config.spec.ts.snap

@@ -11,7 +11,7 @@ projects: await getJestProjectsAsync()
 exports[`createJestConfig should generate files  2`] = `
 "const nxPreset = require('@nx/jest/preset').default;
 
-module.exports = { ...nxPreset }"
+module.exports = { ...nxPreset };"
 `;
 
 exports[`createJestConfig should generate files with --js flag 1`] = `
@@ -25,5 +25,5 @@ projects: await getJestProjectsAsync()
 exports[`createJestConfig should generate files with --js flag 2`] = `
 "const nxPreset = require('@nx/jest/preset').default;
 
-module.exports = { ...nxPreset }"
+module.exports = { ...nxPreset };"
 `;

packages/jest/src/generators/configuration/lib/create-files.ts

@@ -5,12 +5,13 @@ import {
   Tree,
 } from '@nx/devkit';
 import { join } from 'path';
+import type { JestPresetExtension } from '../../../utils/config/config-file';
 import { NormalizedJestProjectSchema } from '../schema';
 
 export function createFiles(
   tree: Tree,
   options: NormalizedJestProjectSchema,
-  presetExt: 'cjs' | 'js'
+  presetExt: JestPresetExtension
 ) {
   const projectConfig = readProjectConfiguration(tree, options.project);
 

packages/jest/src/generators/configuration/lib/create-jest-config.ts

@@ -8,23 +8,34 @@ import {
   type Tree,
 } from '@nx/devkit';
 import { readTargetDefaultsForTarget } from 'nx/src/project-graph/utils/project-configuration-utils';
-import { findRootJestConfig } from '../../../utils/config/find-root-jest-files';
+import {
+  findRootJestConfig,
+  type JestPresetExtension,
+} from '../../../utils/config/config-file';
 import type { NormalizedJestProjectSchema } from '../schema';
 
 export async function createJestConfig(
   tree: Tree,
   options: Partial<NormalizedJestProjectSchema>,
-  presetExt: 'cjs' | 'js'
+  presetExt: JestPresetExtension
 ) {
   if (!tree.exists(`jest.preset.${presetExt}`)) {
-    // preset is always js file.
-    tree.write(
-      `jest.preset.${presetExt}`,
-      `
-      const nxPreset = require('@nx/jest/preset').default;
+    if (presetExt === 'mjs') {
+      tree.write(
+        `jest.preset.${presetExt}`,
+        `import { nxPreset } from '@nx/jest/preset.js';
 
-      module.exports = { ...nxPreset }`
-    );
+export default { ...nxPreset };`
+      );
+    } else {
+      // js or cjs
+      tree.write(
+        `jest.preset.${presetExt}`,
+        `const nxPreset = require('@nx/jest/preset').default;
+
+module.exports = { ...nxPreset };`
+      );
+    }
   }
   if (options.rootProject) {
     // we don't want any config to be made because the `configurationGenerator` will do it.

packages/jest/src/generators/configuration/lib/update-jestconfig.ts

@@ -1,7 +1,7 @@
-import { findRootJestConfig } from '../../../utils/config/find-root-jest-files';
-import { NormalizedJestProjectSchema } from '../schema';
+import { readProjectConfiguration, type Tree } from '@nx/devkit';
+import { findRootJestConfig } from '../../../utils/config/config-file';
 import { addPropertyToJestConfig } from '../../../utils/config/update-config';
-import { readProjectConfiguration, Tree } from '@nx/devkit';
+import type { NormalizedJestProjectSchema } from '../schema';
 
 function isUsingUtilityFunction(host: Tree) {
   const rootConfig = findRootJestConfig(host);

packages/jest/src/generators/init/init.ts

@@ -1,21 +1,24 @@
 import {
   addDependenciesToPackageJson,
+  createProjectGraphAsync,
   formatFiles,
   readNxJson,
   removeDependenciesFromPackageJson,
   runTasksInSerial,
   updateNxJson,
   type GeneratorCallback,
   type Tree,
-  createProjectGraphAsync,
 } from '@nx/devkit';
+import { addPlugin } from '@nx/devkit/src/utils/add-plugin';
 import { createNodes } from '../../plugins/plugin';
+import {
+  getPresetExt,
+  type JestPresetExtension,
+} from '../../utils/config/config-file';
 import { jestVersion, nxVersion } from '../../utils/versions';
-import { isPresetCjs } from '../../utils/config/is-preset-cjs';
 import type { JestInitSchema } from './schema';
-import { addPlugin } from '@nx/devkit/src/utils/add-plugin';
 
-function updateProductionFileSet(tree: Tree, presetExt: 'cjs' | 'js') {
+function updateProductionFileSet(tree: Tree) {
   const nxJson = readNxJson(tree);
 
   const productionFileSet = nxJson.namedInputs?.production;
@@ -40,7 +43,7 @@ function updateProductionFileSet(tree: Tree, presetExt: 'cjs' | 'js') {
   updateNxJson(tree, nxJson);
 }
 
-function addJestTargetDefaults(tree: Tree, presetEnv: 'cjs' | 'js') {
+function addJestTargetDefaults(tree: Tree, presetExt: JestPresetExtension) {
   const nxJson = readNxJson(tree);
 
   nxJson.targetDefaults ??= {};
@@ -53,7 +56,7 @@ function addJestTargetDefaults(tree: Tree, presetEnv: 'cjs' | 'js') {
   nxJson.targetDefaults['@nx/jest:jest'].inputs ??= [
     'default',
     productionFileSet ? '^production' : '^default',
-    `{workspaceRoot}/jest.preset.${presetEnv}`,
+    `{workspaceRoot}/jest.preset.${presetExt}`,
   ];
 
   nxJson.targetDefaults['@nx/jest:jest'].options ??= {
@@ -96,10 +99,10 @@ export async function jestInitGeneratorInternal(
     nxJson.useInferencePlugins !== false;
   options.addPlugin ??= addPluginDefault;
 
-  const presetExt = isPresetCjs(tree) ? 'cjs' : 'js';
+  const presetExt = getPresetExt(tree);
 
-  if (!tree.exists('jest.preset.js') && !tree.exists('jest.preset.cjs')) {
-    updateProductionFileSet(tree, presetExt);
+  if (!tree.exists(`jest.preset.${presetExt}`)) {
+    updateProductionFileSet(tree);
     if (options.addPlugin) {
       await addPlugin(
         tree,

packages/jest/src/utils/config/config-file.ts

@@ -0,0 +1,49 @@
+import { readJson, type Tree } from '@nx/devkit';
+
+export const jestConfigExtensions = [
+  'js',
+  'ts',
+  'mjs',
+  'cjs',
+  'mts',
+  'cts',
+] as const;
+export type JestConfigExtension = typeof jestConfigExtensions[number];
+
+export const jestPresetExtensions = ['js', 'cjs', 'mjs'] as const;
+export type JestPresetExtension = typeof jestPresetExtensions[number];
+
+export function getPresetExt(tree: Tree): JestPresetExtension {
+  const ext = jestPresetExtensions.find((ext) =>
+    tree.exists(`jest.preset.${ext}`)
+  );
+
+  if (ext) {
+    return ext;
+  }
+
+  const rootPkgJson = readJson(tree, 'package.json');
+  if (rootPkgJson.type && rootPkgJson.type === 'module') {
+    // use cjs if package.json type is module
+    return 'cjs';
+  }
+
+  // default to js
+  return 'js';
+}
+
+export function findRootJestConfig(tree: Tree): string | null {
+  const ext = jestConfigExtensions.find((ext) =>
+    tree.exists(`jest.config.${ext}`)
+  );
+
+  return ext ? `jest.config.${ext}` : null;
+}
+
+export function findRootJestPreset(tree: Tree): string | null {
+  const ext = jestPresetExtensions.find((ext) =>
+    tree.exists(`jest.preset.${ext}`)
+  );
+
+  return ext ? `jest.preset.${ext}` : null;
+}

packages/js/src/generators/library/files/jest-config/jest.config.__ext__

@@ -20,7 +20,7 @@ if (swcJestConfig.swcrc === undefined) {
 
 <% if(js) {%>module.exports =<% } else { %>export default<% } %> {
   displayName: '<%= project %>',
-  preset: '<%= offsetFromRoot %>jest.preset.js',
+  preset: '<%= offsetFromRoot %><%= jestPreset %>',
   transform: {
     '^.+\\.[tj]s$': ['@swc/jest', swcJestConfig],
   },

packages/js/src/generators/library/library.ts

@@ -603,10 +603,12 @@ function replaceJestConfig(tree: Tree, options: NormalizedSchema) {
   if (tree.exists(existingJestConfig)) {
     tree.delete(existingJestConfig);
   }
+  const jestPreset = findRootJestPreset(tree) ?? 'jest.presets.js';
 
   // replace with JS:SWC specific jest config
   generateFiles(tree, filesDir, options.projectRoot, {
     ext: options.js ? 'js' : 'ts',
+    jestPreset,
     js: !!options.js,
     project: options.name,
     offsetFromRoot: offsetFromRoot(options.projectRoot),
@@ -1013,4 +1015,12 @@ function logNxReleaseDocsInfo() {
   });
 }
 
+function findRootJestPreset(tree: Tree): string | null {
+  const ext = ['js', 'cjs', 'mjs'].find((ext) =>
+    tree.exists(`jest.preset.${ext}`)
+  );
+
+  return ext ? `jest.preset.${ext}` : null;
+}
+
 export default libraryGenerator;

packages/node/src/generators/e2e-project/e2e-project.spec.ts

@@ -1,3 +1,5 @@
+import 'nx/src/internal-testing-utils/mock-project-graph';
+
 import { Tree } from '@nx/devkit';
 import { createTreeWithEmptyWorkspace } from '@nx/devkit/testing';
 import { applicationGenerator } from '../application/application';

packages/node/src/generators/e2e-project/e2e-project.ts

@@ -28,6 +28,7 @@ import {
   replaceOverridesInLintConfig,
 } from '@nx/eslint/src/generators/utils/eslint-file';
 import { logShowProjectCommand } from '@nx/devkit/src/utils/log-show-project-command';
+import { findRootJestPreset } from '@nx/jest/src/utils/config/config-file';
 
 export async function e2eProjectGenerator(host: Tree, options: Schema) {
   return await e2eProjectGeneratorInternal(host, {
@@ -90,6 +91,7 @@ export async function e2eProjectGeneratorInternal(
     });
   }
 
+  const jestPreset = findRootJestPreset(host) ?? 'jest.preset.js';
   if (options.projectType === 'server') {
     generateFiles(
       host,
@@ -99,6 +101,7 @@ export async function e2eProjectGeneratorInternal(
         ...options,
         ...names(options.rootProject ? 'server' : options.project),
         offsetFromRoot: offsetFromRoot(options.e2eProjectRoot),
+        jestPreset,
         tmpl: '',
       }
     );
@@ -127,6 +130,7 @@ export async function e2eProjectGeneratorInternal(
         ...names(options.rootProject ? 'cli' : options.project),
         mainFile,
         offsetFromRoot: offsetFromRoot(options.e2eProjectRoot),
+        jestPreset,
         tmpl: '',
       }
     );

packages/node/src/generators/e2e-project/files/cli/jest.config.ts__tmpl__

@@ -1,7 +1,7 @@
 /* eslint-disable */
 export default {
   displayName: '<%= e2eProjectName %>',
-  preset: '<%= offsetFromRoot %>/jest.preset.js',
+  preset: '<%= offsetFromRoot %><%= jestPreset %>',
   setupFiles: ['<rootDir>/src/test-setup.ts'],
   testEnvironment: 'node',
   transform: {
@@ -10,5 +10,5 @@ export default {
     }],
   },
   moduleFileExtensions: ['ts', 'js', 'html'],
-  coverageDirectory: '<%= offsetFromRoot %>/coverage/<%= e2eProjectName %>',
+  coverageDirectory: '<%= offsetFromRoot %>coverage/<%= e2eProjectName %>',
 };

packages/node/src/generators/e2e-project/files/server/common/jest.config.ts__tmpl__

@@ -1,7 +1,7 @@
 /* eslint-disable */
 export default {
   displayName: '<%= e2eProjectName %>',
-  preset: '<%= offsetFromRoot %>jest.preset.js',
+  preset: '<%= offsetFromRoot %><%= jestPreset %>',
   globalSetup: '<rootDir>/src/support/global-setup.ts',
   globalTeardown: '<rootDir>/src/support/global-teardown.ts',
   setupFiles: ['<rootDir>/src/support/test-setup.ts'],