React Visual regression

Usually, we only test the javascript part of our components, leaving all styles behavior uncovered. We should test the responsiveness of our components, CSS ellipsis, empty props as well.

This package is based on Pupetter, keeping the browser ready, and handling tests with different pages in order to optimize performance.

Also will use the emulate tools from Pupetter to allow check our responsive designs without having to handle all resolutions on our code, only knowing if we want mobile, tablet or desktop test.

Usage

Install

npm install react-visual-regression

Use

import { render } from "react-visual-regression";
 
render(component, options);

Default options

 
import * as devices from "puppeteer/DeviceDescriptors";
 
options = {
  // Path to .css / .scss file
  stylesheet: undefined;
  device: devices['iPhone X'],
  bodyPadding: 10
}

Device Emulation Select a device from the following list: https://github.com/GoogleChrome/puppeteer/blob/master/lib/DeviceDescriptors.js userAgent, width, height, deviceScaleFactor will be automatically used.

Integration Example

Usage with jest-image-snapshot:

import React from "react";
import { render } from "react-visual-regression";
 
const component = (
  <div>
    <h1>The Component</h1>
  </div>
);
 
describe("Test Component", () => {
  it("has no visual regressions", async () => {
    const image = await render(component, {
      stylesheet: "../../style.css"
    });
 
    expect(image).toMatchImageSnapshot();
  });
});

Real world example reusing settings

I recommend this folder structure for your components

my-component.tsx /.jsx                => your component
my-component.scss / .css              => your styling
my-component.test.tsx /.jsx           => convencional javascript unit testing
my-component.visual.test.tsx / .jsx   => visual regresion unit testing

With this pattern you can select when to run your visual regression tests with:

To run all tests

jest

To run only visual regresion tests

jest --testPathPattern="visual.test.tsx"

To ignore visual regresion tests

jest --testPathIgnorePatterns="visual.test.tsx"

Full Example

import React from "react";
import path from "path";
import { createDevice, imageSnapshotConfig } from "../../src/index";
import * as devices from "puppeteer/DeviceDescriptors";
import { toMatchImageSnapshot } from "jest-image-snapshot";
 
expect.extend({ toMatchImageSnapshot });
 
const cardComponent = (
  name: string,
  disabled: boolean = false
): React.ReactElement => {
  const disabledClass = disabled ? "disabled" : "";
 
  return (
    <div className={`card ${disabledClass}`}>
      <h1>Hello, {name}</h1>
    </div>
  );
};
 
describe("Test Component", () => {
  const stylesheet = path.resolve(__dirname, "../data/sample.css");
 
  const iPhoneRender = createDevice({
    stylesheet,
    device: "iPhone X"
  });
 
  const iPadRender = createDevice({
    stylesheet,
    device: "iPad"
  });
 
  beforeEach(() => {
    jest.setTimeout(10000);
  });
 
  it("should be responsive", async () => {
    const componentWithLargeText = cardComponent("Mike");
    expect(await iPhoneRender(componentWithLargeText)).toMatchImageSnapshot(
      imageSnapshotConfig("iPhone-responsive")
    );
    expect(await iPadRender(componentWithLargeText)).toMatchImageSnapshot(
      imageSnapshotConfig("iPad-responsive")
    );
  });
 
  it("should be responsive with large texts", async () => {
    const componentWithLargeText = cardComponent(
      "Juan Moreno y Herrera-Jiménez"
    );
    expect(await iPhoneRender(componentWithLargeText)).toMatchImageSnapshot(
      imageSnapshotConfig("iPhone-largeText")
    );
    expect(await iPadRender(componentWithLargeText)).toMatchImageSnapshot(
      imageSnapshotConfig("iPad-largeText")
    );
  });
 
  it("should show goshted elements when disabled", async () => {
    const componentWithLargeText = cardComponent("Mike", true);
    expect(await iPhoneRender(componentWithLargeText)).toMatchImageSnapshot(
      imageSnapshotConfig("iPhone-disabled")
    );
    // For this case we can skip different devices :)
    // expect(await iPadRender(componentWithLargeText)).toMatchImageSnapshot();
  });
});

Benchmark

Follow up how this library was improving over the versions.

0.0.8 => 212 snapshots on 288s (about 4.5 minutes)