Angular >=13

Angular 13 introduces ESM package format for Angular packages. jest-preset-angular currently supports testing with Jest in CommonJS mode with Angular 13 using default preset. Jest ESM support with Angular 13 is new and may have issues.

Starting from v11.0.0, jest-preset-angular introduces a few extra changes to be able to run Jest with Angular 13:

• ng-jest-resolver is introduced as a custom Jest resolver to resolve .mjs files.

• moduleFileExtensions is updated to include mjs files as accepted module format.

• transformIgnorePatterns is added to inform Jest to transform .mjs files.

• transform is updated to include .mjs extension to transform to CommonJS codes.

Migration steps from Angular < 13

• Upgrade the project to Angular 13 following guide

• If one is using the default preset as following:

// jest.config.js
module.exports = {
  preset: 'jest-preset-angular',
};

there are no migration steps required

• If one is NOT having preset: 'jest-preset-angular' in Jest config, the config needs to be updated with new values for resolver, transformIgnorePatterns and transform:

// jest.config.js
module.exports = {
  // ...other options
  moduleFileExtensions: ['ts', 'html', 'js', 'json', 'mjs'],
  resolver: 'jest-preset-angular/build/resolvers/ng-jest-resolver.js',
  transformIgnorePatterns: ['node_modules/(?!.*\\.mjs$)'],
  transform: {
    '^.+\\.(ts|js|mjs|html|svg)$': 'jest-preset-angular',
  },
};

Using ES Modules

ES Modules support is new and may encounter issues. See example-app-v13 for an example with tests that run using ESM, and using ESM + isolated.

Your jest.config.js should be changed to something like:

const { pathsToModuleNameMapper } = require('ts-jest/utils');
const { paths } = require('./tsconfig.json').compilerOptions;

/** @type {import('ts-jest/dist/types').InitialOptionsTsJest} */
module.exports = {
  preset: 'jest-preset-angular/presets/defaults-esm',
  globals: {
    'ts-jest': {
      useESM: true,
      stringifyContentPathRegex: '\\.(html|svg)$',
      tsconfig: '<rootDir>/tsconfig-esm.spec.json',
    },
  },
  moduleNameMapper: {
    ...pathsToModuleNameMapper(paths, { prefix: '<rootDir>' }),
    tslib: 'tslib/tslib.es6.js',
  },
  setupFilesAfterEnv: ['<rootDir>/setup-jest.ts'],
};

Before upgrading to ng13 and switching to ES Modules, your setup-jest.ts file most likely uses the preset setup-jest, like the following:

// setup-jest.ts
import 'jest-preset-angular/setup-jest';
import './jest-global-mocks';

The jest-preset-angular/setup-jest file doesn't work with ESM, because it uses require. For now you should skip using this file, and replace the contents of your setup-jest.ts with:

// setup-jest.ts
import 'zone.js';
import 'zone.js/testing';
import './jest-global-mocks';

import { getTestBed } from '@angular/core/testing';
import { BrowserDynamicTestingModule, platformBrowserDynamicTesting } from '@angular/platform-browser-dynamic/testing';

getTestBed().initTestEnvironment(BrowserDynamicTestingModule, platformBrowserDynamicTesting());

Potential issues with Angular 13 ESM package format and workaround

Cannot find modules error when importing any deep paths from Angular ESM format packages

• Angular 13 ESM package format makes Jest resolution not able to resolve the correct .mjs files. Even though we introduced ng-jest-resolver as a part of the preset, this resolver won't work for all scenarios. One might get Jest error like

Cannot find module '@angular/common/locales/xx' from 'src/app/app.component.spec.ts'

To fix this issue, one needs to add mjs to moduleFileExtensions as following

// jest.config.js
module.exports = {
  // ...other options
  moduleFileExtensions: ['ts', 'html', 'js', 'json', 'mjs'],
};

If the issue still persists, you might need to configure moduleNameMapper or extend the behavior the default resolver of this preset.

Usage with Angular libraries which are built with Angular CLI 13

Besides, the changes in Angular packages themselves, Angular libraries which are built with Angular CLI 13 also introduce ESM package format. Similar to Angular packages, Jest doesn't understand .mjs files which are in these new format libraries in Jest CommonJS mode.

To fix this issue, one should modify transformIgnorePatterns to be as following:

// jest.config.js
module.exports = {
  // ...other options
  transformIgnorePatterns: ['node_modules/(?!.*\\.mjs$)'],
};