Visual Regression Testing for React Native Applications

Why Visual Regression Testing Matters

Visual regression testing is essential for ensuring that your app’s UI looks and functions as expected. With the rise of mobile devices, users expect a seamless experience across various platforms. Visual regression testing helps you catch issues that might not be immediately apparent, such as misaligned elements or incorrect font sizes.

Setting Up React Native Owl

Before we dive into writing tests, let’s set up React Native Owl. First, create a new React Native project using the following command:

npx react-native init rnOwlRegression

Next, install React Native Owl using npm or yarn:

npm install --save-dev react-native-owl

Create an owl.config.json file at the root level of your project with the following configuration:

{
  "testEnvironment": "jsdom",
  "moduleNameMapper": {
    "^react-native$": "react-native-web"
  }
}

Writing Your First Test

Create a __tests__ folder at the root level of your project and add a Home.owl.js file inside it. This is where we’ll write our first test:

import React from 'eact';
import { render } from 'eact-native-owl';
import HomeScreen from '../HomeScreen';

describe('HomeScreen', () => {
  it('renders correctly', async () => {
    const tree = await render();
    expect(tree).toMatchSnapshot();
  });
});

This test renders the HomeScreen component and takes a snapshot of it. If the snapshot matches the baseline, the test passes.

Running Tests

To run the test, use the following command:

npx react-native-owl test

This will generate a build of your app and run the test in the emulator. If there are no preset baselines, it will create new baselines.

Adding Another Test

Let’s add another test for the Gallery page:

import React from 'eact';
import { render, fireEvent } from 'eact-native-owl';
import GalleryScreen from '../GalleryScreen';

describe('GalleryScreen', () => {
  it('renders correctly', async () => {
    const tree = await render();
    expect(tree).toMatchSnapshot();
  });

  it('navigates to next screen', async () => {
    const tree = await render();
    const nextButton = tree.getByTestId('next-button');
    fireEvent.press(nextButton);
    expect(tree).toMatchSnapshot();
  });
});

This test navigates to the next screen by pressing the next button and takes a snapshot of the resulting screen.