@cerner/terra-toolkit-docs/lib/terra-dev-site/tool/jest-config-terra/About.a.tool.mdx

Contains documentation for packages in the terra-toolkit monorepo

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# Jest Config Terra

This package provides Terra's recommended jest configuration.

Features:
* An extended Jsdom test environment that:
  * provides a mock implementation for `matchMedia`.
  * provides a mock implementation for `scrollIntoView`.
  * Sets the dir tag on the html element.
* Clears mocks after every test by default.
* Sets up code coverage.
* Specifies test matchers to not match on terra-dev-site files.
* Supports mono repos using a 'packages' directory.
* Maps png, css, scss, and svg files to the [identity-obj-proxy](https://github.com/keyz/identity-obj-proxy).
* Maps terra-aggregate-translations locale files to a mock implementation. This removes the need to run terra-aggregate-translations prior to jest testing.


## What is Jest

"Jest is a delightful JavaScript Testing Framework with a focus on simplicity" - [Jest](https://jestjs.io/)

## Installation

To install the module:

```shell
npm install jest --save-dev
npm install @cerner/jest-config-terra --save-dev
```

## Usage
To extend `jest-config-terra` add a `jest.config.js` file to the root of your project, require `@cerner/jest-config-terra` and export the config. `jest-config-terra` does not support extending configuration in the package.json file.

### jest.config.js

```js
const jestConfig = require('@cerner/jest-config-terra');

module.exports = jestConfig;

```
## Adding configuration

Sometimes it is necessary to add additional configuration. In those instances we've found the cleanest option is to spread the config on a new object and subsequently add overrides where appropriate. For instance this example will import regenerator runtime when setting up test files.

```js
const jestConfig = require('@cerner/jest-config-terra');

module.exports = {
  ...jestConfig,
  setupFiles: [
    'regenerator-runtime',
  ],
};

```

## Enzyme and Testing Library: React

[Enzyme](https://enzymejs.github.io/enzyme/) and [Testing Library: React](https://testing-library.com/docs/react-testing-library/intro) are two popular packages intended to help test react components. `jest-config-terra` can support either and the choice of which package to use is left up to consumers. Testing Library: React requires no additional setup. An example of how to setup Enzyme can be seen below.

### jest.config.js

```js
const jestConfig = require('@cerner/jest-config-terra');

module.exports = {
  ...jestConfig,
  setupFiles: [
    './jest.enzymeSetup.js',
  ],
  snapshotSerializers: [
    'enzyme-to-json/serializer',
  ],
};
```

### jest.enzymeSetup.js

```js
// Make Enzyme functions available in all test files without importing
/* eslint-disable import/no-extraneous-dependencies */
import Enzyme, { mount, render, shallow } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';

Enzyme.configure({ adapter: new Adapter() });

global.shallow = shallow;
global.render = render;
global.mount = mount;
```