Articles | August 1, 2023

Functional Testing in Software Development: A Comprehensive Guide to software testing types and Examples

What functional testing is? What is the purpose of functional tests? Read the article!

Functional Testing in Software Development: A Comprehensive Guide to software testing types and Examples

In the rapidly evolving realm of software development, functional testing stands out as a pivotal procedure. This extensive guide aims to unravel the complex world of functional testing, diving into its myriad types, real-world examples, and the advanced tools that streamline this process. Discover the nuances of automating functional tests and get a sneak peek into the future of functional testing. This article is a must-read for all software testers and developers, offering a profound understanding of different testing techniques and the burgeoning role of automation in testing. So, why wait? Let’s embark on this enlightening journey!

Unraveling the concept of functional testing: what is it all about?

The goal of functional testing is to verify that the application is functioning as required in specific conditions. At various levels of testing, the tester checks whether the software works in accordance with the business requirements set by the stakeholders, and whether it meets users’ expectations.

Functional tests are one of the 4 traditional types of tests. They include functional tests, non-functional tests, structural tests and change-related tests. These tests check the activities that the program is designed to perform, or put simply, they check whether the program is doing what it should.

But to check this, we first need to know what the program should do. Traditionally, the answer to this question should be sought in the specification of requirements, documentation, and ultimately, we must rely on our experience.

Functional testing vs. non-functional testing

Functional testing and non-functional testing – are they two sides of the same coin? Not quite. Functional tests focus on the most basic requirements – whether functionalities work as intended.  Non-functional tests are also referred to as quality tests – here the matter is more complicated than in the case of functional tests. Non-functional testing checks parameters such as performance, usability, and reliability. In other words, functional testing ensures that the software system functions as expected, whereas non-functional testing explores how well the system performs.

Types of functional tests and the indispensable role of functional testing in software development

What you need to bear in mind at this stage is that test types and test levels are two separate concepts.

The test types determine their purpose. In this case, it is to check the behavior of the application and verify that it complies with the specifications and user requirements.

The test levels refer to the phases of software development. The basic divisions are unitintegrationsystem and acceptance tests.  In this article, we will not focus on developing this division further, but we must remember that functional tests should be performed at every available level of testing.

Unit testing & how does it function as a type of functional testing?

Functional tests at the level of unit tests are usually the realm of programmers, because they are usually responsible for creating and maintaining them. At this level, they check whether a single method / function does what it should, e.g., whether the appropriate action is triggered or whether the calculations are correct. This is the lowest of the test levels, as the tests themselves should be simple and performed very quickly. Therefore, this level of testing should be the foundation for automatic verification if the software works properly.

Also read: Test Pyramid

Integration tests

Integration tests, on the other hand, can be the realm of both testers and developers. The basic factor here will be the level at which we check the integration. If we verify the integration of individual methods and functions (after checking with unit tests if they work on their own), it will tend to be the domain of programmers.

However, if we test integration at a higher level, e.g., integration between two application modules, this work can (and often should) be carried out by a software tester. This is due to the fact that a developer testing his own code tests his interpretation of the requirements, but not necessarily the correct one. This is not a shot at programmers, but rather an explanation of why you should not test your own solutions.

System tests

Most people consider functional tests at the system level as the default type of tests. System testing means checking software functionality in an integrated environment, where functionalities can be tested end-to-end. It is also the most intuitive level for beginner testers or people who don’t deal with testing.

But that’s not all – since it is end-to-end testing, it is also very important from the perspective of business and stakeholders, because end users will use the software in a very similar way. Often only at this point can we pay attention to the accuracy of the user interface (both compatibility with mockups and the simplicity of use) and the issue of presenting data to the user. At this level, we can finally check the accessibility of the product for people with disabilities, which is especially important for testers working in public institutions.

Acceptance testing

Acceptance testing is the last stage of testing, which is usually performed on the finished product, by end users, or perhaps by or with the contribution of a client. Functional tests are carried out at this level to finally confirm and approve that the resulting product meets the requirements. It is also the last chance to find defects before handing the product over to end users and the final call to check the compliance of the product with the legal requirements. What is a test pyramid? What, when and how to test?

Read also: User Acceptance Testing (UAT) – Why is it important

How do we perform functional tests?

We have discussed functional tests at different levels, but let’s answer the question of how to perform them. As is often the case with testing, the best answer is that  it depends. Tests at all levels, except for unit tests, can be performed manually more or less successfully.

In the case of integration tests, we will often need additional software to help, but this does not change the fact that well-designed tests can be performed manually.

Test Automation and functional testing: what’s the connection?

We can cover all the previously mentioned test levels with automatic tests. This allows for effective regression testing and also builds trust in the product, as it is regularly checked for correct operation (automatic tests are not for finding errors, but to make sure that functionalities that have already worked keep on doing so).

When to automate your functional tests

The most important business paths during acceptance tests are worth checking manually so we can rest assured that the product is ready to be made available to users. It is worth utilizing automated tests during acceptance testing to limit repetitive work (e.g., redirects with multiple language versions, translations, etc.).

White-box testing or black-box testing techniques?

We already know what functional tests are, what their purpose is, what levels we should perform them at and who can perform such tests. It’s time to answer the question of  what the right way to determine how to test our functional features is.

Tests based on documentation

As I mentioned, functional tests check the correctness of the software in terms of customer requirements, but also in terms of compliance with user requirements.

Compliance with customer requirements

Let’s focus on meeting customer requirements at the beginning. These requirements are usually included in the specification, mock-ups and other forms of documentation. Designing tests based on documentation means the use of black box techniques in practice. Beginner testers often do not even know that they use the popular black box techniques described above when designing tests. This is because the basic techniques are simple and intuitive.

Meeting user expectations

The second part of functional tests is to check whether they meet user expectations. Here the experience of a tester is vital. By that, I mean both testing and industry experience. In these tests, we rely on techniques based on experience – guessing errors, exploratory tests or using checklists.

To sum up, testers have a range of different techniques, some of which require intuition, and others experience. The common denominator for them is the result: well-designed tests which allow us to find defects or raise the level of confidence in the quality of the software.

Is it worth taking an interest in functional software testing?

As part of the functional testing of the application, testers are responsible for testing functions at different levels. The techniques used to find errors create significant opportunities for development and specialization.

Essential Takeaways: What Should You Remember About Functional Testing?

As we conclude this comprehensive guide, let’s recap the key points:

  • Functional testing is pivotal to verify that a software system operates correctly.
  • There’s a clear distinction between functional and non-functional testing.
  • Numerous types of functional testing exist, each with its unique purpose and application.
  • A variety of functional testing tools are available to streamline and automate testing.
  • The future of functional testing lies in increased automation and the use of AI-based techniques.

He has been working in Inetum for over 4 years now as a software tester. In private life, he is an enthusiast of cinema and beer revolution. Believes that testing is an ability of asking adequate questions and preventing bugs is more important than searching for them.

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