Visual Regression Testing with Playwright

 🎯 Visual Regression Testing with Playwright

Visual Regression Testing is a way to check if your application’s user interface (UI) changes unexpectedly between versions. It helps catch layout shifts, color changes, broken buttons, or missing elements that traditional functional tests might miss.


Playwright is a powerful end-to-end testing tool from Microsoft. With Playwright, you can not only test user interactions but also perform visual comparisons by taking screenshots of your app and checking for differences.


🛠 What You Need

Node.js (installed from https://nodejs.org)


Playwright installed


Optional: A test runner like Jest or Playwright Test (built-in)


🔧 Step 1: Install Playwright

In your project folder, run:


bash

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npm init -y

npm install -D @playwright/test

npx playwright install

This installs Playwright and its supported browsers.


📸 Step 2: Write a Visual Regression Test

Create a test file, e.g., visual.test.js:


js

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const { test, expect } = require('@playwright/test');


test('homepage UI should not change', async ({ page }) => {

  await page.goto('https://example.com');


  // Take and compare screenshot

  expect(await page.screenshot()).toMatchSnapshot('homepage.png');

});

Here’s what’s happening:


The test navigates to a webpage


It takes a screenshot


It compares the screenshot to a baseline image called homepage.png


🖼 Step 3: Generate Baseline Images

Run the test for the first time:


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npx playwright test

Playwright will automatically save a baseline screenshot in:


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tests/screenshots/visual-test/homepage.png

Next time you run the test, it will compare the new screenshot to the baseline. If there’s a mismatch, the test fails.


🔍 Step 4: View Visual Differences

If a test fails due to UI changes, Playwright shows:


The expected (baseline) image


The actual screenshot


A diff image that highlights what changed


You can review these images in the test results folder and decide:


If the change is expected, update the snapshot


If it’s a bug, fix the UI


Update the snapshot manually:


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npx playwright test --update-snapshots

🧪 Optional Enhancements

🧱 Limit Screenshot Scope

You can compare only a specific part of the page:


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const element = await page.$('header');

expect(await element.screenshot()).toMatchSnapshot('header.png');

🖥 Run Headless or Headed

Default is headless (no browser UI)


Add --headed to see the browser open during test:


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npx playwright test --headed

✅ Summary

Step What it Does

Install Playwright Sets up test environment

Write test Captures and compares UI screenshots

Run tests Detects any unexpected UI changes

Review diffs Highlights visual bugs in your web app


💡 Why Use Playwright for Visual Testing?

Easy screenshot comparisons


Multi-browser support (Chrome, Firefox, Safari)


Built-in test runner and reporters


Fast and reliable automation

Learn Playwright Training Course in Hyderabad

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Using Playwright in a Kubernetes Environment

Using Playwright with AWS Lambda

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