What Is Front End Testing?
Front end testing is performed to check the functionality and usability of an application’s GUI. It usually involves validating menus, forms, buttons, and other elements of the application that are visible to end-users.
A simple front end test would check the alignment of GUI elements or verify whether input fields accept the specified characters. Another example would be checking the application’s navigation or page load speed.
The Need for Front End Testing
Here’s how front end testing improves the functionality and performance of web-based applications.
- Detecting Client-Side Performance Issues
Most developers place more focus on optimizing functionalities within the server-side of an application. While this is important, testing the front end allows QA teams to evaluate the product from a user point of view.
Through front end tests, development teams can pinpoint problems on the client-side to ensure they do not jeopardize critical workflows in the application.
- Validating Application Behavior on Different Browsers and Systems
Front end testing plays a vital role when it comes to verifying the behavior of web applications on different operating systems, browsers, and devices. It helps validate the functioning and responsiveness of the application over different system architectures.
This is especially important since advancements in client-side development coupled with modifications in browser technologies can lead to compatibility issues. Front end testing is therefore a necessity to make sure a website or application renders the same across different devices and browser engines.
- Improving Quality of User Interaction and Experience
Front end testing helps development teams give users a better experience by optimizing these performance benchmarks. More specifically, it enables users to reduce the application load time, ensure the application’s content is displayed correctly, and give the interface a unified look across different devices and browsers.
Testing and improving these client-side elements increases the quality of applications exponentially. As such, users can enjoy a better and consistent experience across different environments.
- Ensure Seamless Integration of Third-Party Services
Almost every modern application will rely on third-party integrations at some point, especially now that software as a service (SaaS) platforms are increasingly popular. When you integrate other services to your application, a poorly performing script can lead to compromise.
This can cause substantial damage to the user experience as they interact with your application. For this reason, front end tests are indispensable for anyone looking to integrate third-party services to a web application.
- Detecting Client-Side Performance Issues
Factors like usability, navigation, and page load speed are crucial for both users and ranking algorithms on the search engine. A low performing UI can hurt your lead or revenue generation channels, especially if critical workflows are compromised. Think of an e-commerce platform where key workflows such as check-out or adding items to cart are not functioning properly.
The idea here is that a subtle error on the front end of your application can cause irreversible damage. Turning a blind eye towards aspects that may ruin performance is expensive. You need to notice flaws in your systems before end-users do, and this is where front end testing comes into play.
Types of Front End Testing
Front end testing is a broad concept that encompasses a number of testing strategies. This section takes a peek into the most common types.
Front End Unit Testing
Front end unit testing is performed at the lowest level of the software testing pipeline. It usually involves testing individual units such as input validations, calculations, and other UI element actions to ensure they function properly.
Verifying that the units function correctly as independent entities gives development teams assurances that they will work as intended when built into larger front end features. This saves time and simplifies the development process.
Visual Regression Testing
Visual regression tests are unique to the front end. Unlike other types of tests that focus on the code, visual regression testing compares the interface of your application with the corresponding version as expected in the staging or production environment.
This is done by comparing multiple screenshots captured within a headless browser (one that runs on a server). A testing tool that supports image comparison is then used to detect differences between the snapshots.
Integration Testing
Most modern applications are powered by a wide array of microservices. The interaction between these services, if not tested, can potentially ruin the user experience. Performing integration tests ensures communication between your application’s interface and API works smoothly.
It provides insight into the combinational behavior of multiple system elements that are tightly coupled to each other.
Acceptance Testing
Acceptance tests are performed to ensure that user inputs, user flows, and all designated actions on the front end are set up and functioning accordingly. By performing acceptance tests, development teams can be sure that the final model of the application works properly as expected by users.
Cross-Browser Testing
Far too often, users encounter situations where they try to open a website, only to receive a notification that the website does not support the browser they’re using. Sometimes, the website opens, but some functions do not work correctly. In other cases, the browser cannot display the content correctly because responsiveness is lost, or there’s an overlay text in some areas.
Cross-browser testing is done to ensure a web application works as expected in different browsers. The process of verifying compatibility involves running the same set of test cases repeatedly on multiple browsers, making it easy to automate.
Front End vs. Back-End Testing
Back-end testing refers to the type of software tests performed on the business logic and database layers of a web application. It is done to validate the application’s user interface (AUI) in a 3-tier architecture. In most cases, development teams perform back-end tests in the early stages.
While front-end testing is done to check input fields, submit forms, links, buttons, and other UI elements, back-end testing is designed for elements that end users cannot see.
Whether you’re testing simple web applications or complex apps such as ERP systems, back-end testing helps you identify common problems in the server-side of an application. It checks the database for various elements, including the schema, CRUD operations, ACID properties, business rule conformance, security, and performance.
it is important to note that front end tests will vary from one web application to another. Development and QA teams should start by creating a checklist of all front end elements they wish to test. This way, it will be easier to perform exhaustive tests without leaving out the most important elements
For demonstration purposes, we will test the LinkedIn homepage using Perfecto Scriptless. So, we start by creating a new project.
After supplying the initial project details like project name, test name, URL to test, and platform, hit enter and wait for the project to initialize.
This takes a couple of seconds and redirects you to Canvas — the Perfecto Scriptless dashboard where you create, edit, and run your tests.
Here, you can add as many test steps as you wish on a single element. For each step, configure the test parameters and provide any test data required. After editing your test flow, hit the run button, and check the test results.
Performance Optimization in Front End Testing
Years before the introduction of Web 2.0 technologies, most web applications were static, and the vast majority of processing occurred on the server-side. During this time, performance optimization meant optimizing the back end.
However, as applications became more dynamic, there was a greater need to focus on the performance of the front end code. This is in line with the 80/20 rule of web performance.
The implication of this rule is that optimizations made on the client-side will return the greatest performance improvement.
Below are some effective optimization tips you should consider implementing.
Reducing the Number of HTTP Requests
It is common for developers to have multiple CSS and JavaScript files, but it affects the load time negatively. This is because multiple requests will be needed to render the page, which reduces the load time significantly.
A good idea here is to keep the number of HTTP requests required to load the application’s pages to a bare minimum. This involves combining multiple script files into a single file as well as external CSS into another file. This way, two requests will be sufficient to render the content, which is key to fast-loading pages.
CSS Performance Optimization
CSS files are important because they clean HTML documents and give them a professional look. However, overloading a page with CSS plummets its load speed. To optimize front end performance, development teams must eliminate all bloated CSS.
The first approach when optimizing CSS should be using external CSS as opposed to embedded or inline CSS. Using external files reduces the size of HTML pages, thus reducing the bandwidth and increasing the load speed.
You can also optimize front end performance by using CSS Sprites to combine multiple images into a single background file. This reduces the total image size, and subsequently, the download time.
Another way of optimizing CSS is by combining multiple properties using a CSS Shorthand. Instead of having separate declarations for individual properties, as shown in the snippet below, you can combine the properties into one.
Combining the properties to reduce the bandwidth and download time.
element { background: #fff url(image.gif) no-repeat top left; }
Minifying CSS and Script Files
Minification is an optimization technique that involves removing all space characters in the CSS and script files. It helps reduce the total size of your front end code files, hence reducing the download time upon a client request.
While space and indent characters are important for code cleanliness and readability, they expand the file size, thereby increasing the load time. A good way of minifying the files is by using tools such as Google Minify.
Image Optimization
While it is important to use quality imagery, the high resolution can increase the load time significantly. This is because it costs more bandwidth and increases the load time. The most effective way of optimizing images without loss of quality is by using image compression tools such as Kraken, Optimus, and Optimizilla.
Another image optimization strategy is to avoid scaling images in HTML. When you need a 100x100px image, for instance, do not create a 1000x1000px image then scale it in HTML. Additionally, avoid using images to display text content because it will also increase the page load time.
Other effective front end optimization strategies include:
Using a Content Delivery Network (CDN).
Implementing GZip file compression.
Putting scripts at the bottom of your pages.
Using external script files.
Eliminating duplicate scripts.
Reducing Domain Name System (DNS) lookups.
Minimizing cookie size.
Prefetching links and images for quicker access.
Avoiding redirects whenever possible.
Making Ajax cacheable.
Turning off entity tags.
Following the above tips to implement your application’s front-end code will go a long way to improving its overall performance. The process of creating specs and modifying steps involved in a test case is pretty straightforward.
Overcoming Common Front End Testing Challenges
This section takes a closer look at four of the most common front end testing challenges and offers some actionable pointers on how to address the challenges.
Determining the Most Important Front End Elements
Front end testing usually involves testing dozens of UI elements. These include graphics, visible text, formatting, and layout (CSS) as well as functional elements such as buttons, forms, and links. The testing process involves identifying how quickly these features load, how responsive they are to user actions, and how quickly they can execute user requests.
To identify the most important front end features for testing, you can assign rough priorities to the elements. Ideally, you can start by ensuring that basic text and page loads correctly, with key elements placed in the right location. Second, ensure all functional elements are visible and fully responsive. Finally, verify that the graphics and formatting load correctly.
Worth a mention is that the above is just an example of how testers can prioritize their front end testing regime. Some web pages or application modules might require a different approach, such as ensuring graphics load quicker. The most important thing is to ensure the application loads asynchronously. If possible, no UI element should wait for another to load for it to become visible to users.
Simulating the Real-World Environment
This is arguably one of the most common challenges when executing performance-based tests. In most cases, the test environment is controlled, which means the application is not tested under ideal production conditions.
While it is impossible to match the exact user environment, testing teams can set up cases that accurately reflect real-world conditions. This would involve customizing environmental factors that affect page performance.
For instance, you can increase the load on the application in such a way that it reflects concurrent access and multiple user requests to the system. Alternatively, you can limit available memory, CPU performance, or connection speed on the client system.
If you can model these conditions in your test cases, there’s a decent chance that you will reflect the actual production environment. The adjustments you make on the front end will also improve performance in common use cases.
Identifying Where a Problem Lies: Front End or Back End?
It’s not always easy to identify whether a problem is on the client-side or server-side. When an application fails to display a particular element, there could be an issue with the front end code, or something could be wrong on the back end, preventing the server or CDN from delivering content.
A good way to identify where the errors lie is by using front end performance metrics that mark early interactions and those that indicate completed actions. When using a metric such as Time to First Byte (TTFB), which is the time between a client request and the arrival of the first byte on the browser, you can easily identify issues outside the browser environment.
TTFB is an effective benchmark for separating server response time and connectivity speed from front end issues. If the TTFB is short, but there’s a huge delay before the interactive content is loaded, then there’s reasonable evidence to conclude that the delays are on the front end.
Choosing an Appropriate Front End Testing Tool
Today’s software testing market is filled with tons of tools from different vendors. This makes it hard for development teams to pick one that works best for their testing needs and development workflows.
The most important step when selecting a testing tool, whether free or commercial, is assessing the features it provides. Ideally, a good front end testing tool offers the following features:
Easy creation and maintenance of test scripts.
Insight into front end performance metrics.
Screenshot capturing and image comparison capabilities for UI regression testing.
Great reporting capabilities.
Codeless automation for quicker and efficient testing.
Seamless integration into the CI/CD pipeline