Visual Regression Testing with Playwright

In the realm of automated testing, visual regression testing ensures that the user interface (UI) remains visually consistent across application updates. By leveraging Playwright’s advanced testing capabilities, combined with tools like codegen and third-party visual regression tools, testers can automate UI checks with precision and efficiency.

This article explores how to implement visual regression testing using Playwright, including how to use codegen to speed up script creation, why visual testing matters, and best practices to achieve accurate results.

What is Visual Regression Testing?

Visual regression testing ensures that updates to a web application don’t inadvertently alter the visual appearance. It identifies:

Misaligned or broken layouts.
Incorrect fonts, colors, or images.
UI shifts across screen sizes or browsers.

Why Playwright + Codegen for Visual Testing?

Playwright’s codegen feature can auto-generate scripts for navigating your web application, making the setup of visual regression tests faster and less error-prone. By using codegen to record actions, testers can focus on defining and executing their visual checks without manually writing every test step.

Getting Started with Codegen for Visual Regression Testing

1. What is Codegen?

Playwright’s codegen is a powerful feature that records your interactions with a web application and generates a script in JavaScript, TypeScript, Python, or C#. It simplifies the creation of automated tests, including those for capturing screenshots and performing visual comparisons.

2. Using Codegen to Generate Visual Test Scripts

To launch codegen:

npx playwright codegen https://example.com

A browser window will open, allowing you to interact with the site. Playwright records your actions and outputs a script in real time.

3. Example: Generate a Screenshot Script

Start codegen for your application:bashCopy codenpx playwright codegen https://example.com
Perform the actions you want to capture, like navigating to a specific page or interacting with UI elements.
Save the generated script:

const { chromium } = require('playwright');

(async () => {
  const browser = await chromium.launch();
  const page = await browser.newPage();
  await page.goto('https://example.com');
  
  // Capture a screenshot
  await page.screenshot({ path: 'baseline/homepage.png' });
  await browser.close();
})();

4. Extend the Script for Visual Comparison

Once you have a script from codegen, you can integrate it with a visual testing library like Resemble.js:

const resemble = require('resemblejs');
const fs = require('fs');

const baseline = fs.readFileSync('baseline/homepage.png');
const current = fs.readFileSync('current/homepage.png');

resemble(baseline)
  .compareTo(current)
  .onComplete((result) => {
    console.log(`Mismatch: ${result.misMatchPercentage}%`);
    if (result.misMatchPercentage > 1) {
      console.error('Visual changes detected!');
    }
  });

Best Practices for Using Codegen in Visual Regression Testing

Combine Codegen with Manual Tweaks:
While codegen provides a solid foundation, fine-tune the generated script to handle dynamic elements or add assertions specific to your testing needs.
Organize Scripts for Reusability:
Save commonly used navigation and UI interaction scripts for easy reusability across different tests.
Capture Key UI States:
Use codegen to quickly capture key application states, like form submissions or page transitions, to ensure comprehensive coverage.

Conclusion

Integrating codegen into your visual regression workflow with Playwright makes the setup faster, especially for teams new to scripting. Combined with tools like Resemble.js, Playwright empowers testers to maintain UI consistency, catch unintended changes, and automate time-consuming manual checks.

Want to make your Playwright tests faster and more efficient? Check out our in-depth guide on How to Optimize Playwright Scripts for Performance Testing and take your automation to the next level!

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