Functional and Non-functional Testing

Tuesday, 22 November, 2016

QA testing is an important part of software development. In the process of creating applications, testing has a huge role in determining if your applications are performing as you intended. Although everyone thinks that his or her new application is bug-free, it most likely isn’t. Because of that, the testing phase is essential.

Shortening a testing phase is a typical situation. It should not be like that since it is the only way to determine whether an application will function properly before its release date. Testing is sure the best and the only way to know if your product will be success or failure. There are many ways to test applications, but two broad categories of tests are functional and non-functional testing. First, we will discuss each of them and their specifics, and on end about differences between these two tests.

Functional Testing

Functional testing is a way of automated testing that checks all application’s functions. It involves testing the application against the business requirements. The goal of functional testing is to confirm or deny that the application meets the way it was designed to be; it verifies that all the specified requirements are incorporated. All functionality mentioned in the functional specification document have to be covered. Also, here it is important to make sure that the application is meeting the user expectations.

The functional testing process focuses only on what the application does. It is not concerned with an application’s internal details; it does not take care about how it works, why it works or even how well it works. Instead, it checks the program’s functions according to all the available prepared documentation. The primary focus of functional testing is that the system complies with all the requirements. Functional testing ensures that your software is ready for the public release.

Traditionally, a team of testers, independent of the developers, implement functional testing. Testers are checking applications using manual or automated tests, or a mixture of both. For each of the tests that the testers are using they:

They test functions as user commands, searches, data updates or UI functionality. Discovered defects during functional testing are very often related to the user interface or inter-process communication. Functional tests make sure the system behaves correctly from the perspective of the user and according to business and functional requirements.

Positive and negative functional testing are two major categories of functional testing. Applying positive functional testing means using valid inputs to see how the application responds to them and also tests to determine if the outputs are correct. Applying negative functional testing means using invalid inputs, unanticipated operating conditions, and other invalid operations.

Types of functional testing include:

Common practice is applying functional testing on the end of the development cycle, but it can, and it should start much earlier. Even before the testing can apply on an entire system, individual components can be tested. That is a fact because today’s applications need constant updating, changing, and upgrading. Testers need to check the whole life cycle of an application. That will help the developers, who need an independent benchmark for all the development stages. On this way, they will know what they have and have not achieved. Functional testing begins as soon as there is a function to test and continues through the application’s completion and first customer contact. Also, when the software testing is implemented at the beginning of application development cycle, it reduces the time and money expenses.

Non-functional Testing

Non-functional testing is designed to figure out if your product will provide an excellent user experience. It tests the application based on the client and performance requirements.

Before releasing any applications, you must ask yourself:

These are some of the non-functional aspects, but the list goes on. Crucial is that all of these features contribute to the quality of the application. For example, if there is an application which meets all the user requirements perfectly, but it crashes when some big file uploads – this would be bad for user experience and the application would be graded as having a low quality. For example, non-functional tests are used to detect how fast the product responds to a request or how long it takes to do an action.

Non-functional testing includes the following types of testing:

Performance testing evaluates the overall performance of the system. It validates if the system meets the expected response time and values if essential elements of the application meet the desired response time. Load testing checks if the system is working as expected in normal conditions. Test need to be stimulated in the realistic environment on the dedicated server, with a realistic database and repeated with multiple users.

Stress testing evaluates if the system’s performance is good when it is low on resources (low memory, low disk space, multiple users perform same transactions).

Volume testing observes the behaviour of the software when it is involved with a significant amount of data. Limit, where the software fails, needs to be checked. Usability testing evaluates the system for human use – is the application easy to use. User interface testing evaluates Graphical User Interface. Compatibility testing tests are the application compatible with other hardware or software with minimum and maximum configuration. The test needs to be performed with different browsers and with each hardware with minimum and maximum configuration.

Recovery testing evaluates that the application recovers quickly and smoothly in case of any failure. All the data needs to recover from any hardware and software failures. Instability testing confirms that software installs and uninstalls correctly. Documentation testing checks user manuals and other documents.

Security Testing makes sure that the information provided by the user is transmitted securely. Except for the mentioned testing methods, there are a lot of different testing approaches. Non-functional testing is a critical part of quality, and it also requires planning and making a strategy. It is important to use testing tools rather than testing it manually, to make the non-functional testing more effective. The goal is to have a proper coverage of non-functional aspects of the software.

Functional and Non-functional Testing – What’s the Difference?

In software development, there are many ways for quality assurance teams to check and evaluate applications. If they want to make sure that they are delivering the best possible product on the market, there are numerous and different applicable kinds of testing approaches. All of these things can quickly become chaotic. However, there are two main types of testing that we have mentioned – functional and non-functional. They are two sides of the same coin, and it is crucial to genuinely understand the differences between them to utilise them to their fullest extent.

The fundamental difference between functional and non-functional testing is that the functional testing ensures that a product meets business requirements, and non-functional testing wants to see if the product meets performance and client’s requirements. Functional testing determines that the application’s features perform the way they should. Non-functional testing intends to determine if the product behaves correctly. In functional testing, it is all about how well the system performs, and in non-functional testing is how well system responds. Functional testing is based on client’s requirements, while non-functional relies on the customer’s expectations. Functional testing is validating the behaviour, while non-functional testing is validating the performance of the application.

Testing is a complex and time-taking process. It is understandable that testers look for shortcuts to save time in their crowded schedule. It is very easy to think of applying only one, united type of testing and be sure that the produced software will be of quality. That is not true. While the application may fulfil one area’s requirements, it will be missing out on the other parts and needs. Sticking exclusively to functional or non-functional testing is not a smart idea because it can lead to vulnerabilities that break the overall functionality.

Non-functional and functional testing are closely connected, and as a result, you cannot use one without the other. However, some methods used to carry out each will vary from a project to a project. Real QA teams will know how to recognise what is important and according to it, they will use more a  functional or non-functional approach of testing to create the best possible product. With a thorough understanding of testing, they will be able to create a solid testing strategy that directly fits their needs.



In software development, everybody always wants to produce and deliver the best possible product. However, that is not always possible. This is where testing comes in handy. As a vital part of software development process, testing assures that your product meets all the required and expected characteristics. There are many ways to test applications, but the two major categories are the functional and non-functional testing. Every application needs to pass both types of testing to ensure that your consumers have a good experience with your product. Combining the right balance of functional and non-functional testing best practices you can bring a tailor-made solution for every particular project and client situation. A good QA team and good testers will help your company shine in a bright and professional light.

Ana Lozančić

Ana is a content Marketing specialist and blogger. She graduated in Faculty of humanities and social sciences. She enjoys learning and applying knowledge about marketing and social media, covering latest trends and topics about software development subjects.


© 2017, All Rights Reserved. Gauss Development is Gauss Ltd brand.