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.
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.
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:
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.
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.
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 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.
This section explains the most solid reasons to perform visual regression testing in your application. So, keep reading….
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.
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.
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.
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.
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.
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:
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.
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.
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:
Here's an example of how the code might look in Java using the Appium Java client:
```java
import io.appium.java_client.AppiumDriver;
import io.appium.java_client.MobileElement;
import io.appium.java_client.android.AndroidDriver;
import org.openqa.selenium.remote.DesiredCapabilities;
import java.net.URL;
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", "your.app.package");
caps.setCapability("appActivity", "your.app.activity");
// 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
driver.quit();
}
}
```
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.
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.
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.
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.
Here's how users can perform visual regression testing using Appium on LambdaTest:
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.
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.
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).
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 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.
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.
Analyze the VRT results to identify visual differences. LambdaTest provides insights into visual changes, highlighting areas where discrepancies are detected.
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.
Here are some best practices to follow for successful visual regression testing using Appium:
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.
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.
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.
Separate your visual regression tests from functional tests. This allows you to focus solely on visual differences without being distracted by functional issues.
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.
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.
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.
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.
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.
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.
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.
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.
