Getting Started With Visual Regression Testing Using Appium

Getting Started With Visual Regression Testing Using Appium

Today’s software demands a seamless user experience across multiple platforms and devices. One of the most challenging aspects in this domain is maintaining the visual integrity of your application. That's where visual regression testing (VRT) comes into play, offering a streamlined way to catch visual bugs and inconsistencies that could otherwise go unnoticed. For those looking to get started with VRT, Appium offers a robust, scalable framework for automating this kind of testing across a wide range of platforms.

Moreover, services like LambdaTest offer an AI-powered test orchestration and test execution solution for visual regression testing, eliminating the need for teams to set up and manage their own testing infrastructure. This cloud approach provides on-demand access to various real browsers and devices, allowing concurrent testing across multiple environments, reducing test execution time, and ensuring consistency in web application appearance and functionality. LambdaTest also offers detailed testing reports and integration with popular testing frameworks for quick issue identification and resolution.

In this article, we'll explore the basics of getting started with VRT using Appium so that you can elevate your testing strategy to the next level.

What Is Visual Regression Testing?

Visual regression testing is a validation technique employed to ensure that alterations made to an application do not have adverse effects on the visual presentation of the application's user interface (UI). Its primary objective is to confirm that the layout and visual elements comply with predefined expectations, thereby guaranteeing a flawless visual user experience. These visual checks encompass various attributes, such as the position, luminance, contrast, and color of buttons, menus, components, text, and more. This method is also sometimes referred to as visual testing or UI testing.

How Do Visual Regression Tests Work?

At its essence, visual regression testing operates by capturing snapshots of the UI prior to a modification and then contrasting them with screenshots taken afterwards. Any disparities are subsequently highlighted for examination by a test engineer. In practice, there are various techniques for conducting visual regression testing. Some of the most used ones are listed below for you:

Manual Visual Testing

This method involves manual inspection of the UI without the use of specialized tools. Designers and developers dedicate time during each release to visually inspect pages, actively seeking out any visual flaws. While this approach can be laborious and prone to human error when applied to an entire application, it is useful for ad-hoc or exploratory UI testing, especially during the early stages of development.

Pixel-By-Pixel Comparison

This technique scrutinizes the two screenshots at the pixel level, alerting the test engineer to any discrepancies. Pixel comparison, also known as pixel diffs, can identify all potential issues, but it may also flag many inconsequential differences that are imperceptible to the human eye and do not affect usability (e.g., rendering variations, anti-aliasing, or padding/margin differences). The test engineer must meticulously sift through these "false positives" in every test run.

DOM-Based Comparison

This comparison method relies on analyzing the Document Object Model (DOM) before and after a state change and identifying differences. While effective in highlighting code-related modifications within the DOM, it doesn't provide a true visual comparison. It often generates false negatives or positives when the code remains unchanged, but the UI evolves (e.g., dynamic content or embedded content) or when the code changes but the UI remains static. Consequently, test results can be inconsistent and require careful review to prevent overlooking visual defects.

Visual AI Comparison

Visual regression testing employing Visual AI harnesses computer vision to perceive the UI in a manner similar to humans. A well-trained AI can assist test engineers by exclusively flagging differences that a human observer would notice, eliminating the laborious task of addressing "false-positive" issues common in pixel and DOM comparison tests. Additionally, Visual AI can assess dynamic content and identify issues only in unexpected areas or regions.

Reasons To Perform Visual Regression Testing 

This section explains the most solid reasons to perform visual regression testing in your application. So, keep reading….

Ensuring Visual Consistency

Visual regression testing helps ensure that the UI and visual elements of your mobile app remain consistent across different versions, devices, and platforms. This consistency is important for providing a seamless user experience.

Validating Design Changes

When design changes are made to the app, visual regression testing can validate whether these changes were implemented correctly and have not introduced unintended visual issues.

Faster Feedback Loop

Visual regression tests can provide quick feedback to developers and designers, allowing them to address issues early in the development cycle. This reduces the chances of critical visual defects reaching production.

Improved User Experience

Visual glitches and inconsistencies can negatively impact the user experience and tarnish the app's reputation. By catching these issues through visual regression testing, you can enhance user satisfaction.

Regression Testing For UI Libraries

If your app uses third-party UI libraries or frameworks, visual regression testing helps ensure that updates to these libraries do not introduce unwanted visual changes.

Steps To Get Started With Visual Regression Testing Using Appium

Visual regression testing using Appium involves comparing visual elements of an application's user interface to detect any unintended visual changes between different versions of the app. Here are the steps to get started with visual regression testing using Appium:

Step 1: Set Up Appium And Test Environment

First, make sure you have Appium installed and set up on your system. You'll also need the Appium client library for your preferred programming language (e.g., Java, Python). Plus, install any necessary dependencies and tools for your testing environment.

Step 2: Prepare Test Images

Before you can perform visual regression testing, you need a set of baseline images that represent the expected appearance of your app's screens. Capture these baseline images by running your app on various devices/emulators and taking screenshots of each screen. Store these images in a designated folder within your project.

Step 3: Implement Test Scripts

Write test scripts using the Appium client library to automate the process of capturing screenshots and performing visual comparisons. Your test scripts should do the following:

  1. Initialize the Appium driver to launch the app on a specific device/emulator.
  2. Navigate through the app's screens, performing actions that trigger UI changes.
  3. Capture screenshots using Appium's screenshot functionality.
  4. Save the captured screenshots in a separate folder for comparison.

Here's an example of how the code might look in Java using the Appium Java client:


import io.appium.java_client.AppiumDriver;

import io.appium.java_client.MobileElement;


import org.openqa.selenium.remote.DesiredCapabilities;


public class VisualRegressionTest {

public static void main(String[] args) throws Exception {

// Set desired capabilities for the Appium driver

DesiredCapabilities caps = new DesiredCapabilities();

caps.setCapability("platformName", "Android");

caps.setCapability("deviceName", "emulator-5554");

caps.setCapability("appPackage", "");

caps.setCapability("appActivity", "");

// Initialize the Appium driver

AppiumDriver<MobileElement> driver = new AndroidDriver<>(new URL("https://localhost:4723/wd/hub"), caps);

// Perform actions and capture screenshots

// ...

// Save screenshots for comparison

// ..

// Close the driver





Step 4: Implement Visual Comparison Logic

For visual regression testing, you need a mechanism to compare the captured screenshots with the baseline images. You can use image comparison libraries like "Resemble.js" or "Pixelmatch" to perform pixel-by-pixel comparisons and calculate visual differences.

Step 5: Assertion And Reporting

In your test scripts, implement assertions based on the results of the visual comparison. If the visual differences exceed a certain threshold, consider the test as failed. Generate reports detailing the test results, including any visual differences detected.

Step 6: Continuous Integration (CI) 

Integrate your visual regression tests into your CI/CD pipeline to ensure they run automatically whenever there are code changes or new releases. This helps catch visual regressions early in the development process.

Step 7: Maintain Baseline Images

As your app evolves, you'll need to update your baseline images to match the new expected appearance. This ensures that legitimate UI changes aren't mistaken for regressions.

How Users Can Perform VRT Using Appium On LambdaTest?

Here's how users can perform visual regression testing using Appium on LambdaTest:

Set Up LambdaTest Account

To get started, create an account on the LambdaTest platform if you don't have one already. You'll need this account to access their testing infrastructure. Then, make sure to install Appium and all dependencies, as discussed above.

Write Test Scripts

Develop your Appium test scripts to interact with your mobile application. These scripts should include the steps that navigate through your app and capture screenshots of key elements or screens.

Configure LambdaTest Capabilities

Modify your Appium scripts to include LambdaTest-specific capabilities. This includes specifying the desired platform (iOS/Android), browser version, device type, and LambdaTest credentials (username and access key).

Run Tests on LambdaTest

Upload your Appium test scripts to LambdaTest's platform. LambdaTest provides a Selenium grid where you can run your Appium tests. This grid offers a wide range of real devices and browsers for testing.

Execute Tests

Execute your tests on LambdaTest's grid by triggering them from their web-based interface. LambdaTest will execute your tests on the specified mobile devices and browsers, capturing screenshots at various points in your test flow.

Visual Comparison

After test execution, LambdaTest generates screenshots of the application's different states. You can use their built-in visual comparison tool to compare these screenshots against baseline images to identify any visual discrepancies.

Review and Analyze

Analyze the VRT results to identify visual differences. LambdaTest provides insights into visual changes, highlighting areas where discrepancies are detected.

Automated Reporting

LambdaTest offers automated reporting features to track test results over time, making it easier to identify trends and assess the impact of changes on your application's visual appearance.

Best Practices For Successful Visual Regression Testing Using Appium

Here are some best practices to follow for successful visual regression testing using Appium:

Select A Reliable Device And Platform Matrix

Choose a set of devices, operating systems, and screen resolutions that represent the most important combinations used by your target audience. This matrix should cover a diverse range of devices to ensure your app looks consistent across various configurations.

Version Control For Reference Images

Keep a version-controlled repository of reference images that represent the expected visual appearance of your app on different devices and platforms. These reference images will serve as the baseline for comparison during regression tests.

Stable And Consistent Test Environment

Ensure that the test environment is consistent for each test run. This includes using the same OS versions, Appium versions, and libraries across different test runs. Avoid introducing unnecessary changes to the environment that could lead to false positives in your tests.

Isolate UI Changes From Functional Changes

Separate your visual regression tests from functional tests. This allows you to focus solely on visual differences without being distracted by functional issues.

Tolerate Expected Visual Variance

Not all visual differences are bugs. Set a tolerance level for an acceptable visual variance to account for minor UI changes, such as font rendering variations that might not affect the overall user experience.

Dynamic Content Handling

Handle dynamic content such as ads, user-generated content, and real-time data gracefully. You might need to either exclude these elements from comparison or update your reference images to account for these dynamic changes.

Smart Wait Strategies

Implement smart wait strategies to ensure that the app's UI elements are fully loaded before capturing screenshots. This helps avoid false positives caused by incomplete or partially loaded screens.

Parallel Execution

If feasible, run visual regression tests in parallel across multiple devices and platforms. This reduces the overall testing time and ensures faster feedback on potential visual discrepancies.

Automated Reporting And Notifications

Set up automated reporting and notifications to alert the team when visual discrepancies are detected. This ensures quick action and minimizes the time taken to fix issues.

Regular Test Maintenance

As your app evolves, update your reference images and adapt your tests to accommodate visual changes that are intentional. Regularly review and maintain your visual regression tests to ensure they remain relevant.

Review And Validate Findings

Before considering any difference as an actual issue, manually review the screenshots to validate whether the differences are actual bugs or just false positives caused by dynamic content or minor visual changes.

Continuous Improvement

Continuously evaluate your visual regression testing strategy and adapt it as needed. Stay updated with the latest tools, libraries, and best practices to ensure the effectiveness of your testing process.


Whether you are looking to identify unintended changes, reduce manual QA effort, or simply improve visual consistency across different devices and resolutions, VRT is an indispensable tool in your testing arsenal. As with any technology, mastering the nuances takes time, but the benefits in terms of saved time, reduced errors, and a more seamless user experience can be immense. So why wait? Get started with VRT and Appium today, and take your mobile application testing to the next level.

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