@salesforce/sfdx-lwc-jest

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

Versions

To test against the latest Salesforce production instances, use the npm tag appropriate for the current release, e.g.:

yarn add -D @salesforce/sfdx-lwc-jest@winter22
yarn add -D @salesforce/sfdx-lwc-jest@spring22

The npm latest tag corresponds to the latest version of this repo, not necessarily Salesforce production versions.

Invalid sourceApiVersion found in sfdx-project.json

If you see this error while running tests in your Salesforce DX project, it most likely means you are using the incorrect version of this project.

For example, the error message Invalid sourceApiVersion found in sfdx-project.json. Expected 45.0, found 46.0 means this project is targeted to API version 45.0, which maps to Spring '19, but the Salesforce DX project the tests are run in is using API version 46.0, which maps to Summer '19. The version check is done against the projects sourceApiVersion field in the sfdx-project.json file at the top level of the project.

To fix this issue, make sure the most recent version of this project is being used, or switch to the prerelease version, depending on what release your target org is on.

Disabling the sourceApiVersion check

The sourceApiVersion field check is not a perfect check. Projects may be targeting orgs that are on the current release, but still have an older sourceApiVersion value set in their sfdx-project.json file. To disable this check, run tests with the --skipApiVersionCheck flag set.

Note that by doing this, you risk running with an old version of the test runner and your tests may be using an out of date version of the LWC framework. To ensure tests are always run with the proper framework version and configuration, make sure to be on the most recent latest or prerelease tagged version of this package.

Installation

Add this project as a devDependency:

yarn add -D @salesforce/sfdx-lwc-jest

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

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

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.

Usage

`sfdx-lwc-jest [options]` runs Jest unit tests in SFDX workspace

Options:
      --version              Show version number                       [boolean]
      --coverage             Collect coverage and display in output
                                                      [boolean] [default: false]
  -u, --updateSnapshot       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]
      --skipApiVersionCheck  Disable the "sourceApiVersion" field check before
                             running tests. **Warning** By disabling this check
                             you risk running tests against stale versions of
                             the framework. See details here:
                             https://github.com/salesforce/sfdx-lwc-jest#disabli
                             ng-the-sourceApiVersion-check
                                                      [boolean] [default: false]
      --help                 Show help                                 [boolean]

Examples:
  sfdx-lwc-jest --coverage  Collect coverage and display in output
  sfdx-lwc-jest -- --json   All params after `--` are 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.

sfdx-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 sfdx-lwc-jest with the --debug flag.

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

sfdx-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

sfdx-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 sfdx-lwc-jest, modify as you please, and then export the new config.

const { jestConfig } = require('@salesforce/sfdx-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 sfdx-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. We want to test the following template, helloWorld.html.

<template>
    Hello From a Lightning Web Component!
    <lightning-button onclick="{doSomething}"></lightning-button>
    <foo-fancy-button onclick="{doSomethingElse}"></foo-fancy-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/sfdx-lwc-jest/config');
module.exports = {
    ...jestConfig,
    moduleNameMapper: {
        '^foo/fancyButton$': '<rootDir>/force-app/test/jest-mocks/foo/fancyButton',
    },
};

This config 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.

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