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jest-preset-angular

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A preset of Jest configuration for Angular projects.

This is a part of the article: Testing Angular faster with Jest.

Note: This preset does not suport AngularJS (1.x). If you want to set up Jest with AngularJS, please see this blog post.

Installation

yarn add -D jest jest-preset-angular @types/jest
# or
npm install -D jest jest-preset-angular @types/jest

This will install jest, @types/jest, ts-jest as dependencies needed to run with Angular projects.

Usage

In src directory create setupJest.ts file with following contents:

import 'jest-preset-angular';
import './jest-global-mocks'; // browser mocks globally available for every test

Note: feel free to copy the jest-global-mocks.ts file from the test app directory and save it next to the setupJest.ts file.

...and include this in your package.json:

{
  "jest": {
    "preset": "jest-preset-angular",
    "setupFilesAfterEnv": ["<rootDir>/src/setup-jest.ts"]
  }
}

Avoid karma conflicts

By Angular CLI defaults you'll have a src/test.ts file which will be picked up by jest. To circumvent this you can either rename it to src/karmaTest.ts or hide it from jest by adding <rootDir>/src/test.ts to jest testPathIgnorePatterns option.

Exposed configuration

module.exports = {
  globals: {
    'ts-jest': {
      tsConfig: '<rootDir>/tsconfig.spec.json',
      stringifyContentPathRegex: '\\.html$',
      astTransformers: [
        'jest-preset-angular/build/InlineFilesTransformer',
        'jest-preset-angular/build/StripStylesTransformer'
      ],
    },
  },
  transform: {
    '^.+\\.(ts|js|html)$': 'ts-jest',
  },
  moduleFileExtensions: ['ts', 'html', 'js', 'json'],
  moduleNameMapper: {
    '^src/(.*)$': '<rootDir>/src/$1',
    '^app/(.*)$': '<rootDir>/src/app/$1',
    '^assets/(.*)$': '<rootDir>/src/assets/$1',
    '^environments/(.*)$': '<rootDir>/src/environments/$1',
  },
  transformIgnorePatterns: ['node_modules/(?!@ngrx)'],
  snapshotSerializers: [
    'jest-preset-angular/build/AngularSnapshotSerializer.js',
    'jest-preset-angular/build/HTMLCommentSerializer.js',
  ],
};

Brief explanation of config

  • <rootDir> is a special syntax for root of your project (here by default it's project's root /)
  • we're using some "globals" to pass information about where our tsconfig.json file is that we'd like to be able to transform HTML files through ts-jest
  • "transform" – run every TS, JS, or HTML file through so called preprocessor (we'll get there); this lets Jest understand non-JS syntax
  • "testMatch" – we want to run Jest on files that matches this glob
  • "moduleFileExtensions" – our modules are TypeScript and JavaScript files
  • "moduleNameMapper" – if you're using absolute imports here's how to tell Jest where to look for them; uses regex
  • "setupFilesAfterEnv" – this is the heart of our config, in this file we'll setup and patch environment within tests are running
  • "transformIgnorePatterns" – unfortunately some modules (like @ngrx) are released as TypeScript files, not pure JavaScript; in such cases we cannot ignore them (all node_modules are ignored by default), so they can be transformed through TS compiler like any other module in our project.
  • "snapshotSerializers" - array of serializers which will be applied to snapshot the code. Note: by default angular adds some angular-specific attributes to the code (like ng-reflect-*, ng-version="*", _ngcontent-c* etc). This package provides serializer to remove such attributes. This makes snapshots cleaner and more human-readable. To remove such specific attributes use AngularNoNgAttributesSnapshotSerializer serializer. You need to add AngularNoNgAttributesSnapshotSerializer serializer manually (see test app configuration).

AST Transformer

Jest doesn't run in browser nor through dev server. It uses jsdom to abstract browser environment. So we have to cheat a little and inline our templates and get rid of styles (we're not testing CSS) because otherwise Angular will try to make XHR call for our templates and fail miserably.

Angular testing environment setup

If you look at your src/test.ts (or similar bootstrapping test file) file you'll see similarities to setupJest.js. What we're doing here is we're adding globals required by Angular. With the included jest-zone-patch we also make sure Jest test methods run in Zone context. Then we initialize the Angular testing environment like normal.

Snapshot testing

Since version 1.1.0 it's possible to snapshot test your Angular components. Please note it's still under active development and may be a subject of change. You can lookup test app for details

Example:

calc-component.spec.ts

// some initialization code
test('renders markup to snapshot', () => {
  const fixture = TestBed.createComponent(AppComponent);
  expect(fixture).toMatchSnapshot();
});

__snapshots__/calc-component.spec.ts.snap

// Jest Snapshot v1, https://goo.gl/fbAQLP

exports[`CalcComponent should snap 1`] = `
<app-calc
  prop1={[Function Number]}
>
  <p
    class="a-default-class"
    ng-reflect-klass="a-default-class"
    ng-reflect-ng-class="[object Object]"
  >
    calc works!
  </p>
</app-calc>
`;

Removing empty lines and white-spaces in component snapshots

You will immediately notice, that your snapshot files contain a lot of white spaces and blank lines. This is not an issue with Jest, rather with Angular. It can be mitigated via Angular compiler by setting preserveWhitespaces: false

By default it's set to true Angular 7.x, although it may change to be set to false in upcoming versions (if that occurs, you can stop reading right here, because your issue has been already solved)

Your TestBed setup should look like following:

describe('Component snapshot tests', ()=>{
  // you need to turn TS checking because it's an private API
  const compilerConfig = {preserveWhitespaces: false} as any

  beforeEach(() => {
    TestBed.configureCompiler(compilerConfig)
      .configureTestingModule({...});
  });

})

This is indeed very repetitive, so you can extract this in a helper function:

// test-config.helper.ts

import { TestBed } from '@angular/core/testing';

type CompilerOptions = Partial<{
  providers: any[];
  useJit: boolean;
  preserveWhitespaces: boolean;
}>;
export type ConfigureFn = (testBed: typeof TestBed) => void;

export const configureTests = (
  configure: ConfigureFn,
  compilerOptions: CompilerOptions = {}
) => {
  const compilerConfig: CompilerOptions = {
    preserveWhitespaces: false,
    ...compilerOptions,
  };

  const configuredTestBed = TestBed.configureCompiler(compilerConfig);

  configure(configuredTestBed);

  return configuredTestBed.compileComponents().then(() => configuredTestBed);
};

And setup your test with that function like following:

// foo.component.spec.ts

import { async, ComponentFixture } from '@angular/core/testing'

import { configureTests, ConfigureFn } from '../test-config.helper'

import { AppComponent } from './foo.component';

describe('Component snapshots', () => {

  let fixture: ComponentFixture<FooComponent>;
  let component: FooComponent;

  beforeEach(
    async(() => {
      const configure: ConfigureFn = testBed => {
        testBed.configureTestingModule({
          declarations: [FooComponent],
          imports: [...],
          schemas: [NO_ERRORS_SCHEMA],
        });
      };

      configureTests(configure).then(testBed => {
        fixture = testBed.createComponent(FooComponent);
        component = fixture.componentInstance;
        fixture.detectChanges();
      });
    })
  );

  it(`should create snapshots without blank lines/white spaces`, () => {
    expect(fixture).toMatchSnapshot();
  });

})

Troubleshooting

Problems may arise if you're using custom builds (this preset is tailored for angular-cli as firstly priority). Please be advised that every entry in default configuration may be overridden to best suite your app's needs.

Can't resolve all parameters for SomeClass(?)

With Angular 8 and higher, a change to the way the Angular CLI works may be causing your metadata to be lost. You can update your tsconfig.spec.json to include the emitDecoratorMetadata compiler option:

  "compilerOptions": {
    "emitDecoratorMetadata": true

In general, this is related to Angular's reflection and also depends on a reflection library, as e. g. included in core-js. We use our own minimal reflection that satisfy Angular's current requirements, but in case these change, you can install core-js and import the reflection library in your setupJest.ts:

require('core-js/es/reflect');
require('core-js/proposals/reflect-metadata');

Note that this might also be related to other issues with the dependency injection and parameter type reflection.

@Input() bindings are not reflected into fixture when ChangeDetectionStrategy.OnPush is used

This issue is not related to Jest, it's a known Angular bug

To mitigate this, you need to wrap your component under test, into some container component with default change detection strategy (ChangeDetectionStrategy.Default) and pass props through it, or overwrite change detection strategy within TestBed setup, if it's not critical for the test.

// override change detection strategy
beforeEach(async(() => {
  TestBed.configureTestingModule({ declarations: [PizzaItemComponent] })
    .overrideComponent(PizzaItemComponent, {
      set: { changeDetection: ChangeDetectionStrategy.Default },
    })
    .compileComponents();
}));

The animation trigger "transformMenu" has failed

The currenly used JSDOM version handles this, but older versions used before v7 of this preset was missing transform property. To patch it for Angular Material, use this workaround.

Add this to your jestGlobalMocks file

Object.defineProperty(document.body.style, 'transform', {
  value: () => {
    return {
      enumerable: true,
      configurable: true,
    };
  },
});

Reference: angular/components#7101

Absolute imports

TypeScript supports absolute imports. The preset (starting from v3.0.0) by default understands absolute imports referring to src, app, assets and environments directory, so instead:

import MyComponent from '../../src/app/my.component';
import MyStuff from '../../src/testing/my.stuff';

you can use:

import MyComponent from 'app/my.component';
import MyStuff from 'src/testing/my.stuff';

However, if your directory structure differ from that provided by angular-cli you can adjust moduleNameMapper in Jest config:

{
  "jest": {
    "moduleNameMapper": {
      "app/(.*)": "<rootDir>/src/to/app/$1", // override default, why not
      "testing/(.*)": "<rootDir>/app/testing/$1" // add new mapping
    }
  }
}

Custom tsconfig

Override globals object in Jest config:

{
  "jest": {
    "globals": {
      "ts-jest": {
        "tsConfig": "<rootDir>/tsconfig.custom.json",
        "stringifyContentPathRegex": "\\.html$",
        "astTransformers": [
          "jest-preset-angular/build/InlineFilesTransformer",
          "jest-preset-angular/build/StripStylesTransformer"
        ],
      }
    }
  }
}

If you choose to overide globals in order to point at a specific tsconfig, you will need to add the astTransformers to the globals.ts-jest section too, otherwise you will get parse errors on any html templates.

Unexpected token [import|export|other]

This means, that a file is not transformed through TypeScript compiler, e.g. because it is a JS file with TS syntax, or it is published to npm as uncompiled source files. Here's what you can do.

Adjust your tsconfig.spec.json:

Since Angular released v6, the default tsconfig.json and tsconfig.spec.json have been changed. Therefore, jest will throw an error

    ({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,global,jest){import 'jest-preset-angular';
                                                                                             ^^^^^^
    SyntaxError: Unexpected token import
      at ScriptTransformer._transformAndBuildScript (node_modules/jest-runtime/build/script_transformer.js:403:17)

What you need to do is adjust your tsconfig.spec.json to add the option "module": "commonjs",

A default tsconfig.spec.json after modifying will look like this

{
  "extends": "../tsconfig.json",
  "compilerOptions": {
    "outDir": "../out-tsc/spec",
    "module": "commonjs",
    "types": [
      "jest",
      "jquery",
      "jsdom",
      "node"
    ]
  },
  "files": [
    "polyfills.ts"
  ],
  "include": [
    "**/*.spec.ts",
    "**/*.d.ts"
  ]

Adjust your transformIgnorePatterns whitelist:

{
  "jest": {
    "transformIgnorePatterns": [
      "node_modules/(?!@ngrx|angular2-ui-switch|ng-dynamic)"
    ]
  }
}

By default Jest doesn't transform node_modules, because they should be valid JavaScript files. However, it happens that library authors assume that you'll compile their sources. So you have to tell this to Jest explicitly. Above snippet means that @ngrx, angular2-ui-switch and ng-dynamic will be transformed, even though they're node_modules.

Allow JS files in your TS compilerOptions

{
  "compilerOptions": {
    "allowJs": true
  }
}

This tells ts-jest (a preprocessor this preset using to transform TS files) to treat JS files the same as TS ones.

Transpile js files through babel-jest

Some vendors publish their sources without transpiling. You need to say jest to transpile such files manually since typescript (and thus ts-jest used by this preset) do not transpile them.

  1. Install dependencies required by Jest official documentation for Babel integration.

  2. Install @babel/preset-env and add babel.config.js (or modify existing if needed) with the following content:

module.exports = function(api) {
  api.cache(true);

  const presets = ['@babel/preset-env'];
  const plugins = [];

  return {
    presets,
    plugins,
  };
};

Note: do not use a .babelrc file otherwise the packages that you specify in the next step will not be picked up. CF Babel documentation and the comment You want to compile node_modules? babel.config.js is for you!.

  1. Update Jest configuration (by default TypeScript process untranspiled JS files which is source of the problem):
{
  "jest": {
    "transform": {
      "^.+\\.(ts|html)$": "ts-jest",
      "^.+\\.js$": "babel-jest"
    },
  }
}

Observable ... is not a function

Note: This fix is only relevant to Angular v5 and lower.

Since v1.0 this preset doesn't import whole rxjs library by default for variety of reasons. This may result in breaking your tests that relied on this behavior. It may however become cumbersome to include e.g. rxjs/add/operator/map or rxjs/add/operator/do for every test, so as a workaround you can include common operators or other necessary imports in your setupJest.ts file:

import 'jest-preset-angular';

// common rxjs imports
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/switchMap';
import 'rxjs/add/operator/do';
import 'rxjs/add/operator/catch';
// ...

import './jestGlobalMocks';

Allow vendor libraries like jQuery, etc...

The same like normal Jest configuration, you can load jQuery in your Jest setup file. For example your Jest setup file is setup-jest.ts you can declare jQuery:

window.$ = require('path/to/jquery');

or

import $ from 'jquery';
global.$ = global.jQuery = $;

The same declaration can be applied to other vendor libraries.

Reference: jestjs/jest#708

Configure other JSDOM versions

Jest v26 by default uses JSDOM 16 to support Node 10+.

If you need a different JSDOM version than the one that ships with Jest, you can install a jsdom environment package, e.g. jest-environment-jsdom-sixteen and edit your Jest config like so:

{
  "testEnvironment": "jest-environment-jsdom-sixteen"
}

If you use JSDOM v11 or lower, you might have to mock localStorage or sessionStorage on your own or using some third-party library by loading it in setupFilesAfterEnv.

Reference: https://jestjs.io/docs/en/configuration.html#testenvironment-string, https://github.com/jsdom/jsdom/blob/master/Changelog.md#1200

Using Ionic

If you're testing components that use Ionic v4+, add "node_modules/(?!@ionic/core)" to transformIgnorePatterns in your jest config. Otherwise, you may find that jest hangs up without running any test suites.

Additionally, if you reference any ionic custom element types (i.e. HTMLIonInputElement), add @ionic/core to compilerOptions.types in your tsconfig.spec.json.