In This blog

    In an age where businesses heavily rely on programs and software to keep operations and administration running as smoothly as possible, the investment in digital software is higher than ever. In 2023, nearly 90% of businesses think that technology is critical in achieving an organization’s goals, according to Gartner’s 2023 Global Software Buying Trends Report.

    The heavy reliance on digital software has made QA experts more cautious and in demand more than ever. Before signing a sign-off document, QA experts perform functional testing—a much-needed part of the software testing lifecycle.

    But what exactly is functional testing, and why has it become necessary for software quality control?

    Functional Testing: Best Practices, Types & Examples

    What Is Functional Testing?

    Functional testing is a branch of software testing (the other branch being non-functional testing) that ensures that software is working correctly as per a specific set of tests and requirements.

    Functional testing is a crucial step in software testing. It provides a clear pass-or-fail result by keying in input to achieve a standard output and comparing such output with an expected software output per standard.

    On the other hand, non-functional testing covers everything not included in a functional test, including, but not limited to, stability, usability, scalability, security, reliability, integrity, and efficiency.

    In simple terms, functional testing looks at whether a software does what it is supposed to do. In contrast, a non-functional test verifies the performance of software not otherwise tested in functional testing.

    Why Functional Testing Matters

    Software testing is an integral part of user acceptance. Before accepting and signing off on a user acceptance document, ensuring that all software aspects work as intended for the business is important. This includes testing the software’s response to various conditions and scenarios, assessing the effects of data manipulation, and determining if the results match a specific set of predetermined outputs.

    An example is a business acquiring a new Software as a System (SaaS) payroll program to improve payroll staff efficiency in payroll computation. Before signing a sign-off document, payroll staff and SaaS suppliers should perform functional tests on the new payroll system with the same data as the business’ pre-computed payroll. Functional testing can be considered a success once new system results match with pre-computed payroll (given all other tests are already performed).

    Functional testing ensures that minimal to no errors occur after the independent use of the software, ensuring smooth business operations and efficiency.

    Types of Functional Testing

    Different functional testing types are performed to assess whether the software will successfully address a business’ needs and improve the work experience of its end-users. The different functional testing types include:

    Unit Testing

    Unit testing is the smallest and most detailed part of functional testing, which is usually done in the early developmental stages by the developers of the software. A unit test ensures that each smallest testable unit of software works as planned during the development or coding stage.

    A well-performed unit test helps fix potential bugs in the early developmental stages, avoiding future bugs that could otherwise not be seen without a unit test.

    The unit test comes in two types — manual and automated — and techniques involved in unit testing include statement coverage, decision coverage, branch coverage, condition coverage, and finite state machine coverage.

    Integration Testing

    Integration testing ensures that two or more validated unit tests work coherently when they interact or are used together to achieve a desired outcome.

    Performing integration testing is essential because validated working units that work individually may not necessarily work when grouped. This helps developers find potential defects in code conflicts between individual units that should work together.

    System Testing

    After group interactions are tested through integration testing, system testing ensures that all the software components work together seamlessly to achieve the desired output.

    As a crucial part of the software testing life cycle, a system test is a black box test that compares software output with a predetermined outcome. This test operates and processes real-life or business data based on actual usage to ensure that outcomes are the same as the desired result.

    User acceptance Testing

    User acceptance testing is a critical point in the functional testing process where the end-user decides whether to accept or reject the usability and performance of the software.

    This part of the testing process means that end-users or business owners have validated that the software is working correctly and accurately and that system developers have performed all necessary tasks and adjustments to tailor the system satisfactorily to client needs.

    Smoke Testing

    Also called build verification testing or confidence testing, a smoke test is conducted to ensure the developers’ new build is ready for the next testing step.

    A smoke test ensures that all the critical components work properly and seamlessly so that developers can avoid major blockages and issues in the crucial areas of the software.

    Sanity Testing

    While a smoke test ensures that software is ready for the next testing process, a sanity test verifies the accuracy of specific functionalities and whether they are working as expected.

    A smoke test mainly tests the readiness of the entire application, while a sanity test only checks specific functions.

    Interface Testing

    It’s easy to confuse integration testing and interface testing as both testing features verify the seamless performance of an application. The main difference is that while an integration test verifies if two or more working individual units work together as a group, an interface test tests the communication between several interfaces or system software.

    An interface test ensures communication between the system and the user, allowing developers to check whether servers are working correctly, errors are identified, users are sent an error message, and systems can handle network failure between an application and a website.

    Regression Testing

    A regression test is important for developers to ensure that any changes made between testing methods have not impacted other functionalities or that they do not introduce new bugs and problems within the system.

    Methodologies of Functional Testing

    There are several functional testing tools and methodologies to make sure that software is working as intended:

    Equivalence Test

    Equivalence tests or equivalence class partitioning segregate test data into partitions expected to generate the same result. This is mainly used to test a range in an input field. When one partition succeeds in the test, other partitions will also succeed. When one fails, the others will also fail.

    The equivalence test helps efficiently test huge chunks of data into manageable partitions and a smaller number of test cases, especially with a large range of values.

    Boundary Value Test

    Boundary value test verifies the behavior of a system when data limits are implemented in partitions. You test the boundaries between partitions and look for defects when inputting values within data limits and ranges.

    An example of a boundary value test is inputting 5, 7, 8, and 11 characters on a password with a limited range of 6 to 10 characters.

    End-User or System Test

    As the name suggests, the end-user or system tests conduct a total test of an entire system’s functionality from start to finish, following an end-user customer journey, to ensure that all system components are working as intended.

    Decision-Based Test

    During function testing, a developer may perform decision-based tests throughout the process. A decision-based test creates test cases based on certain conditions, ensuring appropriate error messages and functions are done based on each test case.

    Ad Hoc Test

    As the name suggests, ad hoc tests are performed as needed without any prior plans. The goal of ad hoc tests is to see what cannot be seen when usual testing techniques and methodologies are performed, including testing unusual activities that may happen to an end-user.

    Ad hoc tests usually do not follow a predesigned plan or behavior, testing an application’s limits and functionalities for random and exploratory activities within the system.

    Best Practices for Functional Testing

    Functional testing is critical before user acceptance testing, as this step ensures that all systems are working correctly. However, functional testing won’t deliver proper results when not used properly or when the right tests are not made.

    Here are some ways to make sure that functional tests deliver accurate results:

    Layout your test cases properly

    Planning your test cases and methods is critical to ensuring that your testing methods yield effective results.

    Each type of application may require specific tests that may not be necessary for other applications. Identifying which test, what to test, when to test, and how to test at specific parts of the development of the application to the implementation process is critical in a smooth journey for the developers and the end users.

    Documentation is critical

    At every point of the development and implementation, documenting any pertinent issue or change made at any time is crucial to ensure that all team members know all the steps made during the process. This helps developers easily track anything that may have caused a potential bug or problem.

    Communication between team members and end users

    Most software implementations fail because of the lack of proper communication between developers and end-users. Software issues can easily be overlooked and forgotten once they are not addressed immediately, which can cause even more problems when trying to track the source of the problem.

    For an effective testing process, developers and users must immediately communicate any error or potential error that may arise and address such concerns as soon as possible.

    Follow the set guidelines properly

    Aside from ad hoc testing, it is crucial for developers to strictly follow a standard set of rules when it comes to functional testing, especially naming conventions, documentation, testing techniques, and testing orders.

    Some tests may not work correctly when another test isn’t done beforehand, so following the set rules when applying testing techniques is necessary, especially early on in the process.

    AI & Automation

    With AI dominating every facet of the world—from AI chatbots, AI content generators, and AI contract review software — software testing will also greatly benefit from AI functionalities. While manual testing and human touch cannot be eliminated, functional testing automation tools will help automate testing processes through test scripts, ensuring quicker and more accurate results.

    Agile Development

    The rise of agile development will help produce an even faster and more accurate continuous testing process. With a better continuous testing process, the entire development process is tested from development to implementation, ensuring that all processes work correctly.

    Internet of Things (IoT)

    The world is now run by IoT or the Internet of Things. This refers to a network of interrelated devices like cars, phones, laptops, and smartwatches. Software and functional testing should be ready to perform functional tests on the interoperability of programs and applications across a vast network of devices.


    Both developers and end users must pay great attention to functional testing and plan and perform effective functional testing methods that will help verify if products and software are working as intended.

    Proper functional testing will help eliminate any significant repairs and bug fixes that may otherwise be costly for the end user and halt the efficiency of business operations, which is why developers and end-users must work hand in hand to ensure that software testing is done with the proper guidance and approval from both parties.

    PBS LogoDXC Technology LogoBoots LogoMcAffee LogoNCR LogoRoblox LogoAIA LogoEnvisionHealthcare LogoWendy's Logoeasyjet LogoAST LogoUCSF Logo
    PBS LogoDXC Technology LogoBoots LogoMcAffee LogoNCR LogoRoblox LogoAIA LogoEnvisionHealthcare LogoWendy's Logoeasyjet LogoAST LogoUCSF Logo
    About the author
    Jesse Galanis

    Jesse Galanis

    Jesse is a professional writer whose aim is to make complex concepts easy to understand. He strives to provide quality content that assists people in everyday life.

    Related resources


    Taming the Chaos: How to Manage Testing in Complex & Robust Environments


    The 2024 State of Testing™ Report is now live!

    Resource center
    In This blog
      mail twitter linkedin facebook