jest-preset-angular

What is jest-preset-angular?

jest-preset-angular is a Jest preset configuration for Angular projects. It simplifies the setup and configuration of Jest for testing Angular applications, providing necessary configurations, transformers, and environment settings.

What are jest-preset-angular's main functionalities?

Setup and Configuration

This feature provides a preset configuration for Jest, making it easier to set up Jest in Angular projects. The code sample shows how to configure Jest to use jest-preset-angular in the Jest configuration file.

module.exports = { preset: 'jest-preset-angular', setupFilesAfterEnv: ['<rootDir>/setup-jest.ts'] };

Transformers

jest-preset-angular includes transformers to handle TypeScript and Angular templates. The code sample demonstrates how to configure Jest to use ts-jest for transforming TypeScript and HTML files.

module.exports = { transform: { '^.+\.(ts|html)$': 'ts-jest' } };

Global Mocks

jest-preset-angular provides global mocks for common Angular dependencies, such as Angular's testing utilities. The code sample shows how to import jest-preset-angular to include these global mocks in your tests.

import 'jest-preset-angular';

Other packages similar to jest-preset-angular

karma

Karma is a test runner for JavaScript that works well with Angular. Unlike jest-preset-angular, which is a Jest preset, Karma is a standalone test runner that can be configured to work with various testing frameworks, including Jasmine and Mocha.

angular-testing-library

angular-testing-library is a set of utilities for testing Angular components. It focuses on testing user interactions and component behavior, similar to jest-preset-angular, but it is not a Jest preset and can be used with different test runners.

ng-mocks

ng-mocks is a library for creating mocks of Angular components, directives, and services. It complements jest-preset-angular by providing additional mocking capabilities, but it is not a preset configuration for Jest.

README

jest-preset-angular

A preset of Jest configuration for Angular projects.

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

Usage

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

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

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

"jest": {
  "preset": "jest-preset-angular",
  "setupTestFrameworkScriptFile": "<rootDir>/src/setupJest.ts"
}

Exposed configuration

{
  "globals": {
    "__TS_CONFIG__": "src/tsconfig.spec.json",
    "__TRANSFORM_HTML__": true
  },
  "transform": {
    "^.+\\.(ts|js|html)$": "<rootDir>/node_modules/jest-preset-angular/preprocessor.js"
  },
  "testRegex": "(/__tests__/.*|\\.(test|spec))\\.(ts|js)$",
  "moduleFileExtensions": [
    "ts",
    "js",
    "html"
  ],
  "moduleNameMapper": {
    "app/(.*)": "<rootDir>/src/app/$1",
    "environments/(.*)": "<rootDir>/src/environments/$1"
  },
  "transformIgnorePatterns": [
    "node_modules/(?!@ngrx)"
  ]
}

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
• "testRegex" – we want to run Jest on files that matches this regex
• "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
• "setupTestFrameworkScriptFile" – 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.

Preprocessor

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.

I used a scrappy regex to accomplish this with minimum effort, but you can also write a babel plugin to make it bulletproof. And btw, don't bother about perf here – Jest heavily caches transforms. That's why you need to run Jest with --no-cache flag every time you change it.

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 jest-zone-patch we also make sure Jest test methods run in Zone context. Then we initialize the Angular testing environment like normal.

Troubleshooting

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

Absolute imports

TypeScript supports absolute imports. The preset by default understands all absolute imports referring to src 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 'testing/my.stuff';

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

{
  "jest": {
    "moduleNameMapper": {
       "(.*)": "$1", // override default if it causes problems
       "testing/(.*)": "<rootDir>/app/testing/$1"
    }
  }
}

Custom tsconfig

Override globals object in Jest config:

{
  "jest": {
    "globals": {
      "__TS_CONFIG__": "src/tsconfig.custom.json",
      "__TRANSFORM_HTML__": true
    }
  }
}

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 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 transforemed, 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.

Observable ... is not a function

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';