@lwc/jest-preset/README.md

# lwc-jest-preset

Tools to assist with testing Lightning Web Components (LWC) with Jest. This project provides 2 services: preset Jest configuration for testing LWC components, and stubs for common external libraries used in LWC components.

## Requirements

-   Node 8.x
-   NPM 5.x
-   Yarn >= 1.0.0

## Usage

### Jest Preset Configuration

1. Install `lwc-jest-transformer`. This package runs LWC components through the LWC compiler.

    `yarn add -D lwc-jest-transformer`

1. Install `@lwc/jest-resolver`. This package resolves all supported `lwc-*` imports.

    `yarn add -D lwc-jest-resolver`

1. Use this project's preset config. This maps to the settings in `jest-preset.json`. Any settings added to your project's own `jest` config will take precedence to entries in the preset.

    ```json
    {
        "jest": {
            "preset": "lwc-jest-preset"
        }
    }
    ```

1. Update the `moduleNameMapper` entry in your Jest config to point to where your LWC components live. For example, use the following to map all components in the `example` and `other` namespaces:

    ```json
    {
        "moduleNameMapper": {
            "^(example|other)-(.+)$": "<rootDir>/src/test/modules/$1/$2/$2"
        }
    }
    ```

1. Create a `__tests__` inside the bundle of the LWC component under test.
1. Create a new test file in `__tests__` that follows the naming convention `<js-file-under-test>.test.js`. See an example in this projects `src/test` directory.
1. Write and run the Jest tests!