What is Functional Testing? Types and Example (Full Guide)

What is Functional Testing?

In functional testing, testers evaluate an application’s basic functionalities against a predetermined set of specifications. Using Black Box Testing techniques, functional tests measure whether a given input returns the desired output, regardless of any other details. Results are binary: tests pass or fail.

Why is Functional Testing Important?

Functional testing is important because, without it, you may not accurately understand whether your application functions as intended. An application may pass non-functional tests and otherwise perform well. Still, if the application doesn’t deliver the key expected outputs to the end-user, it cannot be considered working.

What is the Difference between Functional and Non-Functional Testing?

Functional tests check if the application meets specified functional requirements, while non-functional tests assess aspects like performance, security, scalability, and overall quality. To put it another way, functional testing is concerned with whether key functions are operating, and non-functional tests are more concerned with how the operations take place.

Examples of Functional Testing Types

There are many types of functional tests that you may want to complete as you test your application. 

A few of the most common include:

Unit Testing

Unit testing breaks down the desired outcome into individual units, allowing you to test if a small number of inputs (sometimes just one) produce the desired output. These tests tend to be small and quick to write and execute. Each one is designed to cover a single section of code (a function, method, object, etc.) and verify that code’s functionality.

Smoke Testing

Testers perform smoke testing to verify that the most critical parts of the application work as intended. It’s a first pass through the testing process and isn’t meant to be exhaustive. Smoke tests ensure that the application is operational on a basic level. If it’s not, there’s no need to progress to more detailed testing, and the application can go right back to the development team for review.

Sanity Testing

Sanity testing acts as a cousin to smoke testing, verifying basic functionality to potentially bypass detailed testing on broken software. Unlike smoke tests, sanity tests occur later in the process to confirm whether a new code change achieves its intended effect. This ‘sanity check’ ensures the new code roughly performs as expected. 

Integration Testing

Integration testing determines whether combinations of individual software modules function properly together. Individual modules may already have passed independent tests, but when they are dependent on other modules to operate successfully, this kind of testing is necessary to ensure that all parts work together as expected.

Regression Testing

Regression testing makes sure that the addition of new code does not break existing functionalities. In other words, did your new code cause the quality of your application to “regress” or go backward? Regression tests focus on recent changes and ensure that the whole application remains stable and functions as expected.

User Acceptance Testing (UAT)/Beta Testing

Usability testing involves exposing your application to a limited group of real users in a production environment. Teams use feedback from live users—who have no prior experience with the application and may uncover critical bugs unknown to internal teams—to make further changes before a full launch.

UI/UX Testing 

UI/UX testing evaluates the application’s graphical user interface. The performance of UI components such as menus, buttons, text fields, and more are verified to ensure that the user experience is ideal for the application’s users. UI/UX testing is also known as visual testing and can be manual or automated.

Other classifications of functional testing include black box testing, white box testing, component testing, API testing, system testing, and production testing.

How to Perform Functional Testing

The essence of a functional test involves three steps:

• Determine the desired test input values
• Execute the tests
• Evaluate the resulting test output values

Essentially, when you execute a task with input (e.g., enter an email address into a text field and click submit), does your application generate the expected output (e.g., the user is subscribed and a thank-you page is displayed)?

We can understand this further with a quick example.

Functional Testing Example

Let’s begin with a straightforward application: a calculator. 

To create a set of functional tests, you would need to:

• Evaluate all the possible inputs – such as numbers and mathematical symbols – and design assertions to test their functionality
• Execute the tests (either automated or manually)
• Ensure that the application generates the desired outputs—for example, each mathematical function works as intended, the final result appears correctly in all cases, and the formula history displays accurately.

For more on how to create a functional test, you can see a full guide on how to write an automated functional test for this example.

Functional Testing Techniques 

There are many functional testing techniques you might use to design a test suite for this:

• Boundary value tests evaluate what happens if inputs are received outside of specified limits – such as a user entering a number that was too large (if there is a specified limit) or attempting to enter non-numeric input
• Decision-based tests verify the results after a user decides to take an action, such as clearing the history
• User-based tests evaluate how components work together within an application – if the calculator’s history was stored in the cloud, this kind of test would verify that it did so successfully
• Ad-hoc tests can be done at the end to try and discover bugs other methods did not uncover by seeking to break the application and check its response

Other common functional testing techniques include equivalence testing, alternate flow testing, positive testing and negative testing.

Automated Functional Testing vs Manual Functional Testing

Manual functional testing requires a developer or test engineer to design, create, and execute every test by hand. It is flexible and can be powerful with the right team. However, as software grows in complexity and release windows get shorter, a purely manual testing strategy will face challenges in keeping up a large degree of test coverage.

Automated functional testing automates many parts of the testing process, allowing tests to run continuously without human interaction – and with less chance for human error. Recent improvements in AI mean that an increasing share of the design and analysis load can be handled autonomously with the right tool.

How to Use Automated Visual Testing for Functional Tests

One way to automate your functional tests is by using automated visual testing. Automated visual testing uses Visual AI to view software in the same way a human would, and can automatically highlight any unexpected differences with a high degree of accuracy.

Visual testing allows you to test for visual bugs, which are otherwise extremely challenging to uncover with traditional functional testing tools. For example, if an unrelated change shifts a ‘submit’ button to the far right of the page, making it unclickable for the user yet still technically present with the correct identifier, it would pass a traditional functional test. Visual testing, however, would catch this bug and ensure that functionality remains unaffected by visual regressions.

How to Choose an Automated Testing Tool?

Here are a few key considerations to keep in mind when choosing an automated testing tool:

• Ease of Use: Is it something easy for your existing QA team to use, or easy to hire for? Does it require an extensive learning curve or can it be picked up quickly?
• Flexibility: Can it be used across different platforms? Can it easily integrate with your current testing environment, and does it allow you the freedom to change your environment in the future?
• Reusability/AI Assistance: How easy is it to reuse tests, particularly if the UI changes? Is there meaningful AI that can help you test more efficiently, particularly at the scale you need?
• Support: What level of customer support do you require, and how easily can you receive it from the provider of your tool?

Automated testing tools can be paid or open source. Some popular open source tools include Selenium for web testing and Appium for mobile testing.

Why Choose Automated Visual Testing with Applitools

Applitools has pioneered the best Visual AI in the industry, and it’s able to automatically detect visual and functional bugs just as a human would. Our Visual AI has been trained on billions of images with 99.9999% accuracy. Applitools includes advanced features to reduce test flakiness and save time, even across the most complicated test suites.

You can find out more about the power of Visual AI through our free report on the Impact of Visual AI on Test Automation. Check out the entire Applitools platform and sign up for your own free account today.

Happy Testing!

Keep Learning

Looking to learn more about Functional Testing? Check out the resources below to find out more.

• Applitools Eyes: Modern Functional Testing [Video, 1:40]

• Modern Functional Test Automation Through Visual AI [Free Course]
• Why Should Software Testers Understand Unit Testing? [Blog]
• The End of Smoke, Sanity and Regression [Blog]
• The Impact of Visual AI On Test Automation [webinar recap]
• Cutting-edge Functional UI Testing Techniques [webinar recap]