@salesforce/lwc-jest

Run Jest against Lightning web components in a Salesforce DX workspace environment.

Installation

Add this project as a devDependency:

yarn add -D @salesforce/lwc-jest

Update your project's unit testing script in package.json to execute lwc-jest:

{
    "scripts": {
        "test:unit": "lwc-jest",
        "test:unit:watch": "lwc-jest --watch",
        "test:unit:debug": "lwc-jest --debug"
    }
}

test:unit runs all your tests. test:unit:watch and test:unit:debug run Jest in watch and debug mode (see below).

Alternatively, you can globally install the package and run directly from the command line.

Troubleshooting deasync Installation Errors

This project has a transitive dependency on deasync to compile Lightning web components during test runs. Depending on your operating system and Node version combination, deasync may attempt to compile C++ code during installation of this project. This has been known to create issues for some Windows users.

The most common solution on Windows is to globally install windows-build-tools. Run the following as administrator:

npm install --global --production windows-build-tools

If that does not work or you are on a different operating system, follow the instructions in the installation section of the deasync README.

If all of the above fail, try pinning the version of deasync to the latest release using yarn's "resolutions" entry inside the consuming project's package.json file. This approach requires using yarn instead of npm to install and build. Add the following to your package.json and run the yarn command from the consuming project root:

"resolutions": {
    "deasync": "0.1.14"
}

Updating .forceignore

After adding Jest tests, pushing your local files to a scratch org causes errors because the __tests__ directory isn't recognized. To ignore these test files, add this entry to your .forceignore file:

**/__tests__/**

See How to Exclude Source When Syncing or Converting for more details.

Usage

`lwc-jest [options]` runs Jest unit tests

Options:
  --version             Show version number                            [boolean]
  --coverage            Collect coverage and display in output
                                                      [boolean] [default: false]
  --updateSnapshot, -u  Re-record every snapshot that fails during a test run
                                                      [boolean] [default: false]
  --verbose             Display individual test results with the test suite
                        hierarchy                     [boolean] [default: false]
  --watch               Watch files for changes and rerun tests related to
                        changed files                 [boolean] [default: false]
  --debug               Run tests in debug mode
                        (https://jestjs.io/docs/en/troubleshooting)
                                                      [boolean] [default: false]
  --help                Show help                                      [boolean]

Examples:
  lwc-jest --coverage  Collect coverage and display in output
  lwc-jest -- --json   All params after `--` will be directly passed to Jest

Passing Additional Jest CLI Options

To pass any additional Jest CLI options to your run, pass them after the -- flag. All CLI parameters after the flag are passed directly to Jest.

lwc-jest -- --json

See the Jest documentation for all CLI options.

Debug mode

Debug mode lets you easily debug your Jest tests.

• Put a debugger; into your code
• Open chrome://inspect
• Run lwc-jest with the --debug flag.

Pass other parameters to Jest after the -- flag. For example,

lwc-jest --debug -- --no-cache

Debugging in Visual Studio Code

If you prefer to debug inside Visual Studio Code, follow these steps:

• From the Visual Studio Code dropdowns, select Debug > Add Configuration....
• If you're prompted for an Environment choose any value.
• Mac users, replace the contents of the generated launch.json with the following. (for Windows users see the Jest website for launch.json contents).

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Debug Jest Tests",
      "type": "node",
      "request": "launch",
      "runtimeArgs": [
        "--inspect-brk",
        "${workspaceRoot}/node_modules/.bin/jest",
        "--runInBand"
      ],
      "console": "integratedTerminal",
      "internalConsoleOptions": "neverOpen",
      "port": 9229
    }
  ]
}

• Add a jest.config.js file to the root of the Salesforce DX project as described here. You must add this file to run Jest from Visual Studio Code.
• To run tests, press F5 or select Debug > Start Debugging.

Watch mode

Watch mode causes Jest to monitor files for changes and rerun tests related to the changed files. This is a great way to rapidly make component and test changes while monitoring tests results.

Overriding Jest Config

lwc-jest sets up all the necessary Jest configs for you to run tests out of the box without any additional changes. To override any options or set additional ones, create a file called jest.config.js at the root of your Salesforce DX project, import the default config from lwc-jest, modify as you please, and then export the new config.

const { jestConfig } = require('@salesforce/lwc-jest/config');
module.exports = {
    ...jestConfig,
    // add any custom configurations here
};

Resolving External Lightning Web Components

If a Lightning web component isn't located in the local lwc directory of your Salesforce DX project, you must mock it in your Jest tests. This package includes a set of stubs for all components in the lightning namespace.

Lightning Namespaced Component Stubs

This package installs stubs for the lightning base components to the src/lightning-stubs directory. These stubs are used automatically when running tests through lwc-jest. To override the default stub provided for your project, override the moduleNameMapper config as described in Other Component Mocks.

Other Component Mocks

For components from other namespaces, not in your local lwc directory, create your own mock and update the Jest config to map the name of these components to the mock file.

Let's go through an example. Given the following template, helloWorld.html, we want to test:

<template>
    Hello From a Lightning Web Component!
    <lightning-button onclick={doSomething}></lightning-button>
    <foo-fancy-button onclick={doSomethingElse}></foo-button>
</template>

Because it's in the lightning namespace, the lightning-button just works. However, you must write some code to help the Jest resolver find the foo-fancy-button component. First, create a jest.config.js file at the root of the Salesforce DX project workspace and add the following:

const { jestConfig } = require('@salesforce/lwc-jest/config');
module.exports = {
    ...jestConfig,
    moduleNameMapper: {
        '^foo/fancyButton$': '<rootDir>/force-app/test/jest-mocks/foo/fancyButton',
    }
};

This tells Jest to map the import for foo-fancy-button to the provided file. Notice that the first dash is converted to a forward slash and the rest of the component name goes from kebab to camel case. The reason for the forward slash is because the module resolver treats everything before the first dash as the namespace. Here, <rootDir> maps to the root of the Salesforce DX workspace. Note that this file location is not required, just an example.

You also have the freedom to make these mock implementations as sophisticated or simple as you'd like. In this example, we'll keep foo-fancy-button simple with an empty template and no functionality in the .js file, but you can always add whatever markup you'd like or implement functionality like any other Lightning web component.

Finally, we need to create the mock foo-fancy-button files. In the force-app/test/jest-mocks/foo directory create the following files:

<!-- fancyButton.html -->
<template></template>

// fancyButton.js
import { LightningElement, api } from 'lwc';
export default class FancyButton extends LightningElement {
  @api label
  // any other implementation you may want to expose here
}

Testing @wire Adapters

To provision data through @wire adapters in unit tests, use the APIs provided by @salesforce/wire-service-jest-util. These APIs are exposed through this package so you do not need to include another dependency in your package.json.

import {
    registerTestWireAdapter,
    registerLdsTestWireAdapter,
    registerApexTestWireAdapter
} from '@salesforce/lwc-jest';

See the @salesforce/wire-service-jest-util README for further documentation on these APIs.