Frontend Testing: A Guide for 2024

This is making frontend testing a must-have step of the workflow for software development teams to focus on, ensuring the quality of your technology throughout its lifecycle.

Frontend in general covers developing the graphical user interface (GUI) of a website, through the use of different technologies (like HTML, CSS, or JavaScript) so that users can view and interact with that website or web app. Essentially, the frontend is the parts of a digital web product that a user can see and interact with.

Frontend testing, therefore, refers to the checks performed to test the usability and functionality of your application’s GUI. Usually, test cases include the validation of menus, forms, buttons, and other application elements visible to end users.

This article contains everything you need to know about frontend testing, and how you can apply it to your latest technology products and applications.

Why is frontend testing important?

When you’re developing an application, the most important thing is to ensure the developed application works correctly and is safe for production deployment.

This can be achieved by thinking about the most seamless ways a user can take through your app, optimizing the navigational experience.

While you do of course want to ensure a safe production deployment (i.e. that that app simply works), you also want to make sure that the application stays stable throughout the whole cycle of user interaction. That means that you also need to secure edge cases in vulnerable or critical parts of the application, which can include areas like infinite loading times or error states the user won’t be able to exit from.

Protection against regression

The tests you perform to check these things can be either manual or automated, depending on the specific requirements. What you’re essentially doing here is testing the client (browser) part of the application.

For example, if you have a ‘submit’ button, you want to make sure that when this is clicked it actually triggers the relevant action, and links to the data processing happening on the server (though the data processing is of course a backend testing responsibility).

Frontend tests provide your app with strong protection against regression. There might be cases where you write code that helps you deploy huge or complex features but might in return crash some other part of the application that you weren’t aware of.

Double checking the code

It’s not uncommon for teams or even individual developers to forget some code written a while ago in the process, and then to add new code to the existing one that can cause troubles elsewhere in the frontend.

This will be even more visible in projects with multiple developers. With the increasing complexity of modern applications, it’s rare that you’ll be able to deliver a big project alone. No one can simply know everything about every piece of code written by other programmers. And this is why frontend testing is so important - to double check that code is not inconsistent and the frontend functionality is intact.

Trust in the code

You need to build up trust in your code and the final application. Otherwise users may never download your app or delete it after a short time. Whenever a bug appears, found either by your team or users, it should, of course, be fixed - but also covered by an additional test suite so you know it won’t reappear again unexpectedly.

The more you can trust your code, the easier and less stressful deployments will be. Additionally, business leaders will undoubtedly be happier knowing that their application is developing at a stable pace, enabling the company to plan and prepare roadmaps easier.

Live documentation

Another good reason to keep well-maintained tests is that they serve as live documentation. Writing tests requires a proper description of what a specific test (and the component of your application it relates to) does.

In order to run a proper test, you need to add mocks, using the API of components, which can then serve as guidelines for other developers or your teams in the future on how things can be used later.

Additionally, in opposition to hand-written documentation in README files, these guidelines live within your project. What this means is that if a test is outdated, it will probably result in errors which force you to update the documentation - which can sometimes be a forgotten task when handled manually.

Writing test suites can (and probably should) also lead to improving readability and decreasing coupling in the application code. When a developer wants to test a small chunk of application but also needs to spin up a few dependent components and mocks that aren’t necessarily related to the testing, that can be a sign that they need to remodel part of the code. It is a sign that interdependencies between code parts are too tight.

What to test in frontend?

Frontend testing is all geared towards performance optimization and enhancing the user experience. Before the advent of Web 2.0 technologies, most web applications were static.

That’s why the majority of processing was done on the server side, meaning performance optimization was achieved through the backend. Now, with applications becoming more dynamic, there is a greater need to optimize the frontend code.

There are several aspects to focus on when testing the frontend of your application. They include:

• Cross-browser and cross-platform functionality - Checking both the features and responsiveness of your app on different browsers, platforms and devices

• Accessibility - You need to check that everyone can access your application, including those with visual or auditory impairments

• End-to-end checks - are required for checking and confirming the end-to-end workflow of the application (backend to frontend) by mimicking the real-world actions users are likely to take

• Image analysis testing - most websites and apps these days have lots of images on them - from standard display images to logos, infographics and banners. They increase the size of the application significantly, and so you need to run tests to see where you can optimize the images to help the app run faster.

• Cascading Style Sheets (CSS) testing - CSS is used to help build and style the components of an application. While the user never sees the style sheet code, if it is not written properly, they will definitely see the negative effects of it so you need to run tests to ensure the performance of two main CSS elements: syntax and display. While syntax is rather a domain of developer’s day-to-day work, displayed views need to be tested for regression after changes to specific parts of the app.

Challenges of frontend testing

Frontend testing is essential. However, there are some common challenges you need to be aware of and prepare for when handling it.

Determining the most crucial frontend elements

Frontend testing normally includes testing lots of different user interface (UI) elements. These include formatting, visible text, graphics, and style/layout (CSS) as well as all the functional aspects of the app such as buttons, submit forms, and clickable links.

The process here involves testing how responsive these features are; how quickly do they load, what are the response times to user actions, and are they fast enough at executing user requests?

Obviously with so much to test, you need to prioritize the most important frontend features. To do this, assign rough priorities to each of the components, starting by making sure that basic text and pages load easily, with crucial elements in the right place.

Next, look to make sure that all functional elements are visible and respond fully to actions and requests, before finally checking that the formatting and graphics load as they should do.

Simulating the real-world environment

One of the most common challenges of frontend testing is emulating how your app will work in the real world. Your test environment will always be controlled, so it’s hard to get an objective view of how the app is going to act outside of that controlled environment.

While it’s very difficult to match the user’s exact real-world conditions, your testing team can set up cases that closely reflect them by customizing the environmental factors affecting page performance.

For example, you can increase the application load in a way that reflects concurrent access and multiple user requests to the system. Or, you can limit the available memory, CPU performance, or connection speed of the client system. Modeling these conditions within your test cases, there’s a good chance of reflecting the real-world production environment.

Choosing testing tools

Frontend testing requires the use of different testing tools and kits, and you need to pick the right one for the task.

We will discuss some of the best frontend testing tools below, but for now the most important area to consider here is the features the testing tools provide. There are lots of software vendors on the market and it’s hard to spot the differences.

The best frontend testing tools though include:

• Easy creation and maintenance of test scripts
• Performance metrics insights
• High-end reporting capabilities
• Seamless integration
• Automation tools

Automation is essential to effective and fast frontend testing because manual testers cannot be expected to keep running tests with every new update.

Human factors

Leading on from the importance of automation, there are “softer” challenges to take into account in the frontend testing process. And these are human factors.

This doesn’t necessarily mean people making errors in testing, although that can happen. Sometimes, developers might be forced to skip tests for a number of different reasons. Customers may need to speed up the release or resources for it aren’t available at the moment.

Sometimes, usually if done internally, teams might not be aware that frontend tests are needed at all.

Imagine it as a metaphor of a broken window. This theory states that if something is visible and unaddressed, it will most likely be repeated. Namely, if it’s obvious that tests haven’t been run properly or code is written incorrectly, it’s likely that these practices will be replicated in the future, compounding issues with your application. It’s vital therefore to ensure that best frontend testing practices are adhered to at all times.

Best practices in frontend testing

Frontend testing is vital, but it’s also important that you stick to certain principles to ensure best practice when running the tests, otherwise you may not be able to fully rely on the test results. Here are the best practices in frontend testing, categorized as the F.I.R.S.T. principles.

F.I.R.S.T principles

To ensure that you stick to the best practices of frontend testing, you need a framework to follow. Luckily, you can use the F.I.R.S.T. principles for it.

F.I.R.S.T. principles stand for:

• Fast
• Isolated/Independent
• Repeatable
• Self-validating
• Thorough

Most of these are self-explanatory. Tests should be run speedily (at any necessary point of the life cycle), isolated from untested components, easily repeatable for the future, able to validate themselves whether the test has been passed and cover all necessary variables.

Start with the testing pyramid

The testing pyramid is a framework to help development teams create high-quality software. It reduces the time needed for developers to identify any changes negatively impacting their code and supporting building reliable test suites.

The testing pyramid is sometimes referred to as the ‘ test automation pyramid’. It sets out the test types that you should include in automated testing and outlines what sequences and frequency these tests should follow. The aim is to provide immediate feedback, ensuring that code changes do not disrupt existing features.

This testing pyramid is split into three levels:

• Unit tests
• Integration tests
• End-to-end tests

Prioritize frontend elements

As we mentioned earlier, frontend testing means analyzing and verifying hundreds or thousands of UI and functional elements. UI elements include things like formatting, CSS, text, graphics, while functional elements include forms, links, buttons, and so on.

You need to prioritize which of these are tested first to ensure an effective testing process. It’s sensible to test page load speed, basic text, images, and essential functions (e.g., adding items to a shopping cart, payment tools) first, and before moving on to graphics and pop-ups. Check that each of these elements are visible and responsive, and then move on to verifying graphics and layout.

Use real browsers and devices

Using real browsers and devices is an essential aspect of conducting error-free, reliable frontend tests which reflect the real-world environment as much as possible. Avoid using emulators and simulators and save time and resources by using real browsers and devices - this way, you will be able to rely on your software testing results much more.

Types of frontend tests

Since there are different elements to test for the frontend, there are a few different types of tests you can consider running. Each of these focuses on a different component of your frontend and together will ensure successful frontend testing for your application.

Unit testing

Unit testing is the fundamental building block of frontend testing. It analyzes individual components and functions to ensure they’re working as expected. This is crucial for any frontend application, testing your components and features against how you expect them to behave in production, leading to a stable codebase and a reliable app for your customers. You can also use unit testing for things like edge cases and testing APIs.

Acceptance testing

Acceptance testing is carried out to confirm that user inputs, user flows, and any designated actions on the frontend are coded and functioning properly. Development teams perform them to make sure the final model of the application works as it is expected to by end users.

Visual regression testing

Visual regression testing is a uniquely frontend test. Other types of tests focus on code, and can therefore also be run for backend stacks. In turn, visual regression tests compare the actual/existing interface of your application with the corresponding ‘expected’ version to identify any gaps. This is achieved by comparing screenshots from a headless, server-run browser, and a machine is used to conduct image comparison between them, identifying and highlighting any differences.

Accessibility testing

Accessibility testing checks if an application or website is easily usable by every potential user, including individuals with visual impairments or other additional needs. It is sometimes considered a subcategory of usability testing, and ensures that specific, unchangeable conditions don’t prevent anyone from accessing any of the features or functions of the app, and that they can navigate through the interface as easily as anybody else.

Performance testing

Performance testing analyzes your application’s performance within specific parameters including speed, stability, scalability, interoperability and responsiveness. It is crucial to frontend testing as it helps to ensure that the product sustains its desired quality when the user load is increased, and it is fast and responsive to user requests and actions.

End-to-end (E2E) testing

End-to-end testing is used to check and confirm that the flow of the application works as expected from start to finish. It is mainly done by mimicking the actions of a real user within real-world scenarios to ensure smooth communication between the application’s interface and API is running smoothly. Doing so provides insight into the combined behavior of multiple system elements coupled together.

Integration testing

Integration testing in frontend tests is a software testing approach that focuses on verifying the interactions and integration points between various components or modules of a web application's user interface. It ensures that these components work together seamlessly and can involve testing how different parts of the frontend (e.g., UI elements, APIs, and data sources) interact and behave in conjunction with each other, helping to identify issues such as data flow problems, communication errors, and functional integration problems.

Cross-browser testing

Cross-browser testing is performed to confirm that an application works as expected in different web browsers. This process involves running the same set of test cases on different browsers to check that the application is compatible on each one. Because these tests are the same each time, this process can be automated.

Common frontend testing tools

As we’ve already touched upon, there are hundreds - if not thousands - of different vendors out there supplying frontend testing tools, and it can be difficult to decide which one to choose. There is a list of some of the best and most common frontend testing tools for your needs.

Jest

Jest is one of the most popular JavaScript Testing Frameworks with a focus on simplicity. By ensuring your tests have a unique global state, Jest can reliably run tests in parallel. To make things quick, Jest runs previously failed tests first and re-organizes runs based on how long test files take. It also offers powerful code coverage and easy mocking tools.

Selenium WebDriver

Selenium WebDriver is a web framework that allows developers to execute cross-browser tests. It is used for automating web-based application testing to verify compatibility. This tool allows you to choose a programming language to create test scripts for cross-browser testing.

Cypress

Cypress is an end-to-end testing framework for web test automation. It enables frontend developers to write automated web tests in JavaScript, one of the most popular programming languages used for website development. The use of JavaScript makes Cypress an especially attractive tool for developers. In terms of developer experience, Cypress Syntax is incredibly easy to use - sometimes it is literally as simple as writing sentences in English!

WebDriverIO

WebdriverIO is a progressive automation framework built to automate modern web and mobile applications. It simplifies the interaction with your app and provides a set of plugins that help you create a scalable, robust and stable test suite.

WebDriverJS

WebDriverJs is the official Javascript implementation of Selenium, using Selenium's Json-wire-protocol to interact with browsers. WebDriverJS performs basically the same functions as Selenium WebDriver.

TestCafe

Test Cafe is a Node. js end-to-end, free, and open-source automation tool which can be used to test web applications. It works in all popular environments such as Windows, MacOS, and Linux. With easy-to-install features in a single command, you can write scripts in JavaScript or TypeScript.

Puppeteer

A Node library developed by Google for controlling headless Chrome or Chromium browsers, useful for both testing and web scraping.

Enzyme

A JavaScript testing utility for React that simplifies testing React components by providing shallow rendering and assertions.

How to create a frontend testing plan?

So you know what to test, why you need to run the tests and know a few different frontend testing tools. But how do you go about putting your frontend testing plan in place? These are the key steps you should follow:

Define your testing budget

Before you purchase tools or hire test engineers, and decide on a timeline, you need to know what your budget is for testing. Usually, this would have been factored into your initial project budget, but it’s good to check expectations against reality when you get to the testing phase.

Choose your tools

Depending on the components and elements contained within your frontend, different tools may do the job for you. Review your requirements against the list of common tools above, or get in touch with a Netguru expert if you’re unsure.

Set a timeline

What is your project deadline? You need to allow enough time for testing and any amendments prior to final release of the application. While deadlines can be strict and give your development team something to work towards, it’s important to be as flexible as possible. After all, you don’t want to release an app that doesn’t work properly, even if it is released on time.

Define the scope of your project

Again, this is likely factored into your initial project plan, but review it again here. In any application development you need to decide on the extent of testing required.

Does the application need to be perfect when you release it, or is it possible to go into production with a working version and see how users respond? Sometimes user feedback can be as useful as the insights you get from automated tests.

Depending on the answer here, you can define the scope of the project so you don’t use more resources than you need to.

Ready for frontend testing?

As we’ve seen, frontend testing is a crucial activity for a business building a new application or website. It ensures that everything your potential customer sees and interacts with works well, so it can be the difference between a successful product and one that never sells.

It is also quite a complicated process, with lots of tools to choose from, multiple different types and testing and various challenges to overcome. Of course, the scope and budget of your project will impact your frontend testing too, so there’s lots to consider before you get started.

Still unsure? Get in touch with a Netguru expert today to help optimize your frontend performance testing, and empower your development teams to release a successful application to market.