Visual Regression Testing with Playwright: Tips and Tricks

Regression Testing ensures that modifications to the system don’t affect current functionality or coding standards. Nearly all test suites in software development life cycles include them. It is not uncommon for developers to update or modify a part of code and inadvertently break something functioning perfectly.

Visual Regression Testing applies the same concept but looks at the software’s visual features. It compares two photos and automates complex situations, such as when we cannot recognize the items in the DOM tree. However, visual regression can be applied to any website.

Visual Regression Testing also falls under the umbrella of automation testing, which streamlines the process of comparing visual elements to identify any discrepancies introduced by code changes.

This post will review the specifics of using Playwright for visual regression testing and offer helpful hints and techniques to improve your testing procedure.

Overview of Visual Regression Testing

Visual regression testing looks for any inadvertent visual changes in web applications by comparing screenshots taken before and after modifications. It keeps the user experience intact by ensuring that UI elements are consistent across platforms and versions.

Overview of Playwright

Playwright is a powerful open-source automation library developed by Microsoft. It gives developers a standard API to automate many browsers, including Firefox, WebKit, and Chromium, allowing them to carry out a variety of activities, including visual regression testing.

Setting up Playwright for Visual Regression Testing

You can use the following procedures to set up Playwright for visual regression testing:

1. Install Node.js

Make sure your computer has Node.js installed. Node.js is available for download and installation via https://nodejs.org/, the official website.

2. Create a new Node.js project

For your project, make a new directory and use the terminal to navigate into it.

3. Initialize a new Node.js project

Open your terminal and type the following command to launch a brand-new Node.js project:

“` 

npm init -y 

“`

4. Install Playwright

Use the following command to add Playwright as a dependency to your project: npm install playwright.

5. Install Jest (Optional)

Popular testing framework Jest is compatible with Playwright. With the following line, you may install Jest as a development dependency:

  “`

   npm install –save-dev jest

  “`

6. Create Test Files

Playwright can be used to create test files for visual regression testing. You can design distinct files for various application pages or parts.

7. Write Tests

Make tests that utilize Playwright to save the pages and UI elements screenshots from your app. The next, screenshots need to be compared with the baseline screenshots so as to identify any visual changes.

8. Configure Jest (Optional)

You can set Jest up to execute your Playwright tests if you’re using it. You may make a `jest.config.js` file in your project directory and set Playwright as the test environment.

9. Run Tests

The command to run your tests is as follows:

“` 

   npm test 

“`

10. Review Test Results

Examine the test results to find any visual discrepancies between the baseline and current screenshots.

11. Update Baseline Screenshots

You can update the baseline screenshots to reflect the changes in your application if the visual variations are expected.

Using Playwright to Write Your First Visual Regression Test

To write your first visual regression test with Playwright, follow these steps:

1. Install Playwright

Ensure that you have Playwright installed in your project. If not, you can install it by running:

   “`

   npm install playwright

   “`

2. Create a Test File

Create a new JavaScript file for your test suite. For example, you can name it `visual_regression_test.js`.

3. Import Playwright**: 

In your test file, import the necessary modules from Playwright:

   “`javascript

   const { chromium } = require(‘playwright’);

   “`

4. Write Your Test

Write a test function using Playwright to capture screenshots of your application’s UI components. Here’s a simple example:

   “`javascript

   describe(‘Visual Regression Test’, () => {

       let browser;

       beforeAll(async () => {

           browser = await chromium.launch();

       });

       afterAll(async () => {

           await browser.close();

       });

       it(‘should capture a screenshot of the homepage’, async () => {

           const page = await browser.newPage();

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

           await page.screenshot({ path: ‘screenshots/homepage.png’ });

           await page.close();

       });

   });

   “`

5. Run Your Test

You can run your visual regression test by executing your test file. If you’re using a testing framework like Jest, you can configure Jest to run your Playwright tests. Otherwise, you can run the test file directly using Node.js.

6. Review the Screenshots

After running the test, review the screenshots captured by the Playwright. You can visually inspect them to ensure no unexpected changes in your application’s UI.

7. Update Baseline Screenshots

If the screenshots captured during the test match the expected baseline, you can update your baseline screenshots. Otherwise, investigate any unexpected differences and make necessary adjustments to your tests or application code.

By following these steps, you can write your first visual regression test with Playwright and ensure the consistency of your application’s UI across different releases and changes.

Handling Dynamic Content

Managing dynamic content in visual regression testing is essential to producing accurate and trustworthy test results. The Playwright offers several strategies to handle this difficulty successfully. Here’s how to use assertions and comparisons in Playwright and deal with dynamic content:

1. Wait for Elements to Stabilize

Before taking screenshots or assertions, make sure that dynamic elements have loaded using built-in methods like `waitForSelector` or `waitForFunction}.

2. Settle Time

Use the `setTimeout` or `wait` functions to introduce a brief waiting time so that dynamic content can stabilize before capturing screenshots or making comparisons.

3. Identify Stable Elements

To reduce dynamic content’s impact, take screenshots of consistent sections or areas of your application’s user interface.

Implementing Assertions and Comparisons:

1. Pixel-by-Pixel Comparison

Playwright lets you take screenshots and use image modification libraries like Pixelmatch to compare individual pixels. Although it compares photographs finely, this method could be sensitive to small changes in the visuals.

2. Perceptual Diffing Algorithms

Playwright incorporates Image Snapshot Testing with perceptual diffing methods like Pixelmatch or Resemble.js. These algorithms use human vision to examine photos, which reduces false positives and enables more detailed comparisons.

3. Thresholds and Tolerances

Establish thresholds or tolerance levels for picture comparisons to account for small visual discrepancies brought about by dynamic content or different browser and device renderings.

4. Baseline Image Management

Organize a collection of reference photos that illustrate typical user interface conditions. Update baseline pictures regularly to match deliberate UI modifications and maintain stability against dynamic content.

5. Integration with Testing Frameworks

To expedite the execution of tests, assertions, and result reporting for visual regression tests, integrate Playwright with testing frameworks such as Jest or Mocha.

These techniques can help you deal with dynamic content and use Playwright to create strong assertions and comparisons in your visual regression tests. This guarantees the precision and dependability of your tests even when your application’s user interface has dynamic aspects.

Visual Regression Testing Tips and Tricks for Playwright

Using Playwright for visual regression testing might be an effective way to ensure that your web apps’ visual integrity is maintained across modifications. The following pointers will help you get the most out of Playwright’s visual regression testing:

1. Use Screenshot Comparison

You may take screenshots of web pages with Playwright. You can take screenshots of particular components or whole pages during your tests. Utilize these screenshots to compare the code before and after changes.

2. Establish Baseline Screenshots

Take baseline screenshots of your application’s important pages or components before making any modifications. These baseline screenshots will be used as pointers for future comparisons.

3. Implement Automated Testing

Use Playwright to incorporate visual regression testing into your automated test suite. Regression is constant and dependable when tested automatically. Regression testing is guaranteed reliable and consistent across all environments and code modifications, thanks to automated tests.

4. Define Tolerance Levels

Establish tolerance thresholds for visual variations between the baseline and the latest screenshots. For picture comparisons, Playwright offers options to set pixel and percentage tolerances. Adjust these tolerance limits Based on your application’s specifications and the sensitivity of visual changes.

5.  Handle Dynamic Content

During visual regression testing, deal with dynamic content such as advertising, timestamps, and user-generated information. Make sure the content is consistent for comparison by using strategies like stubbing or mocking.

6. Viewport and Device Emulation

Use Playwright’s viewport and device emulation features to test your application’s responsiveness and visual look across a variety of viewports and computing platforms. This guarantees that your application will appear and work properly across a range of devices and screen sizes.

7. Parallel Test Execution

To cut down on test execution time overall, run visual regression tests concurrently. With Playwright’s support for parallel test execution, you may run more tests at once and shorten the feedback loop.

8. Continuous Integration (CI) Integration

If you want to automatically identify visual regressions early in the development lifecycle, incorporate visual regression testing into your CI/CD process. Start visible regression testing with each code push or pull request using continuous integration (CI) tools such as Jenkins, GitHub Actions, Travis CI, or LambdaTest.

With the AI-powered test orchestration and execution platform provided by LambdaTest, you can automate visual regression tests for various devices, operating systems, and browsers. Your CI/CD process can guarantee thorough test coverage and identify any visual differences between environments by integrating LambdaTest with it.

You can use LambdaTest’s APIs or plugins/extensions for widely used CI systems to incorporate them into your CI/CD workflow. During the continuous integration, you may promptly detect and resolve any UI discrepancies before they affect end users by initiating visual regression tests on LambdaTest’s platform.

By combining Playwright’s features and LambdaTest’s capabilities, you can create a strong visual regression testing plan that guarantees the dependability and quality of your web applications in various settings.

9. Custom Matchers and Assertions

By developing unique matchers and assertions for particular visual components or patterns in your application, you can expand Playwright’s functionality. You may effectively spot minor differences and establish specific criteria for visual comparisons with custom matchers.

10. Regular Maintenance

Review and update baseline screenshots frequently to reflect modifications to the functionality or appearance of your program. Update your visual regression tests often to guarantee accurate and trustworthy findings.

Conclusion

In conclusion, Playwright’s Visual Regression Testing offers a reliable way to make sure that the visual components of web applications are high-quality and consistent. Through the utilization of best practices like tolerance levels, baseline screenshots, and dynamic content handling, developers may efficiently identify and address any inadvertent visual modifications. Efficiency and dependability are increased by incorporating visual regression testing into automated processes and making use of tools like viewport emulation and continuous integration. Accuracy is maintained through routine maintenance. Developers can confidently create consistent, high-quality user experiences across platforms and updates with Playwright and appropriate testing techniques.