jest-expo

What is jest-expo?

The jest-expo package is a set of Jest presets tailored for testing Expo applications. It simplifies the setup and configuration needed to test React Native components and other Expo-specific features, making it easier to write and run tests for Expo projects.

What are jest-expo's main functionalities?

Preset Configuration

The jest-expo package provides a preset configuration that you can use in your Jest configuration file. This preset includes all necessary settings to test Expo applications, such as transforming JavaScript and TypeScript files, handling static assets, and mocking native modules.

module.exports = { preset: 'jest-expo' };

Snapshot Testing

Snapshot testing is a feature that allows you to capture the rendered output of a component and compare it to a reference snapshot file. This helps ensure that your UI does not change unexpectedly.

import React from 'react';
import renderer from 'react-test-renderer';
import App from '../App';

test('App snapshot', () => {
  const tree = renderer.create(<App />).toJSON();
  expect(tree).toMatchSnapshot();
});

Mocking Native Modules

jest-expo makes it easy to mock native modules and Expo-specific APIs, allowing you to test components that rely on these modules without needing a physical device or emulator.

jest.mock('expo-constants', () => ({
  manifest: {
    extra: {
      apiUrl: 'https://api.example.com'
    }
  }
}));

Other packages similar to jest-expo

react-native-testing-library

react-native-testing-library is a popular library for testing React Native components. It provides utilities to render components, query elements, and simulate user interactions. Compared to jest-expo, it focuses more on testing the behavior of components rather than configuration and setup.

enzyme

Enzyme is a JavaScript testing utility for React that makes it easier to assert, manipulate, and traverse your React components' output. While it is not specific to React Native or Expo, it can be used in conjunction with other tools to test React Native components. It offers a different approach to testing compared to jest-expo, focusing on shallow rendering and component manipulation.

jest

Jest is a delightful JavaScript testing framework with a focus on simplicity. It works with projects using Babel, TypeScript, Node.js, React, Angular, Vue.js, and Svelte. While jest-expo is built on top of Jest and provides Expo-specific configurations, Jest itself is a more general-purpose testing framework.

README

jest-expo

A Jest preset to painlessly test your Expo apps.

Installation

• yarn add jest-expo --dev or npm i jest-expo --save-dev

• Add the following config to package.json:

  "scripts": {
    "test": "jest"
  },
  "jest": {
    "preset": "jest-expo"
  }
  

• Create a __tests__ directory anywhere you like and a Example-test.js file inside of it, and add this code:

  it('works', () => {
    expect(1).toBe(1);
  });
  

• Run npm test and it should pass

Learning Jest

Read the excellent documentation