Neutrino Jest Preset

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

Features

• 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

Requirements

• Node.js v6.10+
• Yarn or npm client
• Neutrino v7, Neutrino build preset

Installation

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

Yarn

❯ yarn add --dev @neutrinojs/jest

npm

❯ npm install --save-dev @neutrinojs/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

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

npm

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

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

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.

Quickstart

After adding the Jest preset to your Neutrino-built project, 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', () => {
    expect(false).not.toBe(true);
  });
});

Now edit your project's package.json to add commands for testing your application. In this example, let's pretend this is a Node.js project:

{
  "scripts": {
    "test": "neutrino test --use @neutrinojs/node @neutrinojs/jest"
  }
}

Or if you are using .neutrinorc.js, add this preset to your use array instead of --use flags:

module.exports = {
  use: [
    '@neutrinojs/node',
    '@neutrinojs/jest'
  ]
};

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

Yarn

❯ yarn test

 PASS  test/simple_test.js
  simple
    ✓ should be sane (2ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.936s
Ran all test suites.
✨  Done in 2.12s.

npm

❯ npm test

 PASS  test/simple_test.js
  simple
    ✓ should be sane (2ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.972s
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.

Executing single tests

By default this preset will execute every test file located in your test directory ending in the appropriate file extension. Use the command line files parameters to execute individual tests.

Watching for changes

@neutrinojs/jest can watch for changes on your source directory and subsequently re-run tests. Simply use the --watch flag with your neutrino test command.

Coverage reporting

Jest has an integrated coverage reporter, which requires no configuration. To collect test coverage information and generate a report:

❯ neutrino test --coverage

You can also edit your package.json file and create a separate command for generating a coverage report, which can be helpful during continuous integration of your project:

{
  "scripts": {
    "coverage": "neutrino test --coverage"
  }
}

Additional options

You can pass any additional option Jest accepts. See the Jest documentation for more configuration options.

For example, if you want to run tests on the precommit hook with lint-staged, you can run:

npx mrm lintstaged

and update the configuration in your package.json to:

{
  "lint-staged": {
    "*.js": [
      "neutrino lint --fix",
      "neutrino test --findRelatedTests",
      "git add"
    ]
  }
}

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. Use an array pair instead of a string to supply these options.

Example: Turn off bailing on test failures.

module.exports = {
  use: [
    ['@neutrinojs/jest', { bail: false }]
  ]
};

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

Example: Jest setup scripts

module.exports = {
  use: [
    ['@neutrinojs/jest', {
      // 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);
};

Customizing

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.

Rules

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

Name	Description	Environments and Commands
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.

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. Use an array pair instead of a string to supply these options.

Example: Add a custom Babel plugin when testing:

module.exports = {
  use: [
    '@neutrinojs/jest'
  ],
  env: {
    NODE_ENV: {
      test: (neutrino) => neutrino.config.module
        .rule('compile')
        .use('babel')
        .tap(options => merge(options, {
          env: {
            test: {
              plugins: ['custom-babel-plugin']
            }
          }
        }))
    }
  }
};

Contributing

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