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Neutrino Jest Preset

@neutrinojs/jest is a Neutrino preset that supports testing JavaScript projects with the Jest test runner.

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  • Zero upfront configuration necessary to start testing
  • Babel compilation that compiles your tests using the same Babel options used by your source code
  • Source watching for re-running of tests on change
  • Collecting test coverage information and generating report
  • Easily extensible to customize your testing as needed


  • Node.js 10+
  • Yarn v1.2.1+, or npm v5.4+
  • Neutrino 9 and one of the Neutrino build presets
  • webpack 4
  • Jest 24-26


The fastest way to get started is by using the create-project scaffolding tool. See the Create new project docs for more details.

Don’t want to use the CLI helper? No worries, we have you covered with the manual installation.

Manual Installation

First follow the manual installation instructions for your chosen build preset.

@neutrinojs/jest can be installed via the Yarn or npm clients. Inside your project, make sure @neutrinojs/jest and jest are development dependencies. You will also be using another Neutrino preset for building your application source code.


❯ yarn add --dev @neutrinojs/jest jest


❯ npm install --save-dev @neutrinojs/jest jest

Installation: React Testing

Jest is often used in the testing of React components. If you are using this preset in a React application, which most likely means you are using @neutrinojs/react, you should also consider adding React's TestUtils and potentially a higher-level abstraction such as Airbnb's Enzyme. These should be development dependencies of your project.


❯ yarn add --dev react-addons-test-utils enzyme


❯ npm install --save-dev react-addons-test-utils enzyme

See the React's Test Utils documentation for specifics on React testing with this approach.

After that, add a new directory named test in the root of the project, with a single JS file named simple_test.js in it.

❯ mkdir test && touch test/simple_test.js

Edit your test/simple_test.js file with the following:

describe('simple', () => {
  it('should be sane', () => {

Now update your project's .neutrinorc.js to add the @neutrinojs/jest preset. In this example, let's pretend this is a Node.js project:

const node = require('@neutrinojs/node');
const jest = require('@neutrinojs/jest');

module.exports = {
  use: [node(), jest()],

Create a jest.config.js file in the root of the project, that will be used by the Jest CLI:

// jest.config.js
const neutrino = require('neutrino');

process.env.NODE_ENV = process.env.NODE_ENV || 'test';

module.exports = neutrino().jest();

Then add these scripts entries to your package.json to simplify running Jest:

  "scripts": {
    "test": "jest",
    "test:watch": "jest --watch"

Run the tests, and view the results in your console:


❯ yarn test

 PASS  test/simple_test.js

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        3.265s
Ran all test suites.


❯ npm test

 PASS  test/simple_test.js

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        3.265s
Ran all test suites.

To run tests against files from your source code, simply import them:

import thingToTest from '../src/thing';

For more details on specific Jest usage, please refer to their documentation.

Project Layout

@neutrinojs/jest follows the standard project layout specified by Neutrino. This means that by default all project test code should live in a directory named test in the root of the project. Test files end in either _test.js, .test.js, _test.jsx, or .test.jsx.

Executing single tests

By default this preset will execute every test file located in your test directory ending in the appropriate file extension. Pass specific test filenames to the Jest CLI to override this.

Watching for changes

@neutrinojs/jest can watch for changes on your source directory and subsequently re-run tests. Simply pass --watch to the Jest CLI (for example by using the test:watch scripts entry above).

Coverage reporting

Jest has an integrated coverage reporter, which requires no configuration. To collect test coverage information and generate a report, use the CLI's --coverage option.

Additional CLI options

See the Jest CLI options documentation.

Preset options

You can provide custom options and have them merged with this preset's default options, which are subsequently passed to Jest. You can modify Jest settings from .neutrinorc.js by overriding with any options Jest accepts. In a standalone Jest project this is typically done in the package.json file, but @neutrinojs/jest allows configuration through this mechanism as well. This accepts the same configuration options as outlined in the Jest documentation.

Example: Turn off bailing on test failures.

const jest = require('@neutrinojs/jest');

module.exports = {
  use: [jest({ bail: false })],

You might need to instruct Jest to load some setup scripts (e.g. when you use Enzyme).

Example: Jest setup scripts

const jest = require('@neutrinojs/jest');

module.exports = {
  use: [
      // setup script for the framework
      setupTestFrameworkScriptFile: '<rootDir>/test-setup.js',
      // and / or shims
      setupFiles: ['<rootDir>/shim.js'],
test-setup.js and shim.js _test-setup.js for the example above_
const Enzyme = require('enzyme');
const EnzymeAdapter = require('enzyme-adapter-react-16');

// Setup enzyme's react adapter
Enzyme.configure({ adapter: new EnzymeAdapter() });
_shim.js for the example above_
global.requestAnimationFrame = (callback) => {
  setTimeout(callback, 0);


To override the test configuration, start with the documentation on customization. @neutrinojs/jest creates some conventions to make overriding the configuration easier once you are ready to make changes.


The following is a list of rules and their identifiers which can be overridden:

Name Description NODE_ENV
compile Compiles JS files from the test directory using adopted Babel settings from other build presets. Contains a single loader named babel. all

Override configuration

By following the customization guide and knowing the rule, and loader IDs above, you can override and augment testing by providing a function to your .neutrinorc.js use array. You can also make this change from the Neutrino API when using the use method.

Example: Add a custom Babel plugin when testing:

const jest = require('@neutrinojs/jest');

module.exports = {
  use: [
    (neutrino) => {
      if (process.env.NODE_ENV === 'test') {
          .tap((options) =>
            merge(options, {
              env: {
                test: {
                  plugins: ['custom-babel-plugin'],


This preset is part of the neutrino repository, a monorepo containing all resources for developing Neutrino and its core presets and middleware. Follow the contributing guide for details.