What is Functional Testing? [Definition, Types, Tools]

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What is Functional Testing? [Definition, Types, Tools]

Sameeksha Medewar
Last updated on May 22, 2024

    A team of professionals tests a particular software product to meet specific quality standards and specified requirements in software testing. All the stakeholders, including a product owner, sponsors, end-users, and investors, specify their requirements during the specification phase. The development team creates a document containing all the Software Requirements Specification (SRS) requirements. This document assists the development team in understanding how to implement the software product. Also, SRS makes it easier for the development team to simplify the development process and ensure customer satisfaction. SRS consists of all types of requirements. There are two broad categories of software requirements, namely functional and non-functional. Functional requirements are functionalities that end-users expect to have in the software product. On the other hand, non-functional requirements are the quality constraints that the software system should meet. When we need to check whether the software product meets all the functional requirements or not, we make use of functional testing. Similarly, when we need to verify that the software product complies with all non-functional requirements, we need to perform non-functional testing. This article intends to provide you with an in-depth insight into functional testing. Also, it will make you familiar with the advantages, disadvantages, and different types of functional testing. Finally, you will learn about some of today's most popular functional testing tools. So, let us get started!

    What is Functional Testing?

    Functional testing is software testing that tests the software product against functional requirements or specifications. It is a black-box testing technique where testers examine the system's functionalities without knowing the software product’s internal structure and implementation details. Since it is a black-box testing technique, testers primarily focus on the requirements or specifications of the software product rather than the actual source code. It is usually associated with what the software product does. The primary purpose of this type of software testing is to ensure that each function of the software product behaves in conformance with the specified requirements. Moreover, the testing team tests each function of the software product by providing input data, producing the output, and comparing the actual results with the expected ones. Furthermore, this testing involves checking the user interface, database, application program interface (API), security, and many such functionalities of the software product under development.


    As mentioned above, the primary objective of this testing is to validate the software product for its functionalities. It primarily focuses on testing the following:

    • Basic Usability: It checks whether the end-users can navigate easily and hassle-free through screens.
    • Accessibility: It involves testing the accessibility of the software product for end-users.
    • Mainline Function: It majorly focuses on testing the main features of the software product.
    • Error Condition: It checks whether the suitable error messages are displayed or not.


    Here are the salient features of functional testing:

    • It is a quality assurance process where testers create test cases on the basis of the software product’s requirements or specifications.
    • It checks whether each function of the software product works as intended. Also, it ensures that the software product is in compliance with the requirements that stakeholders specify.
    • It is a black-box testing technique. Hence, there is no need for testers to know the software product's internal structure and implementation details.
    • This testing primarily focuses on what the system does rather than how the system does.
    • It is specification-based testing.


    Now that we know the concept of functional testing let us understand it with one real-world example. Let us consider an eCommerce website, where a customer adds various products to the cart and checks out. Later, the website should take the customer to the payments page to make the payment. Once the customer chooses the desired payment method, the website should take them to bank security verification. After the payment process is completed, the customer should receive an email regarding the order confirmation, price, expected delivery date, and other information. Functional testing ensures that all the steps above, ranging from checkout to order confirmation email, occur in a correct sequence, without any errors.


    The following are the remarkable benefits of functional testing:

    • It produces a defect-free product.
    • It ensures customer satisfaction by checking whether the product meets all the requirements.
    • This type of testing is essential for validating the software product's functionality. Moreover, it checks whether all the functions of the system work correctly.
    • It enhances the quality of the software product and ensures its security and safety.


    Some common drawbacks of functional testing are as follows:

    • It may miss the logical or critical error in the software product.
    • There is a possibility that testers may conduct redundant testing, i.e., they may test the same function twice.
    • It cannot guarantee that the software product is ready to go live.

    Types of Functional Testing

    The following are the types of testing that fall under functional testing:

    1. Unit Testing

    Unit testing is a type of software testing which involves testing each component of the software product, called unit, separately. It ensures that each component or unit of the software product under development functions as expected. Here, a unit can be any function, method, object, or procedure in the software product's source code. Generally, software developers are responsible for carrying out unit testing. However, many organizations allow testers to perform unit testing. They isolate the code of a specific unit or component and test it to check its correctness. Furthermore, unit testing is the first level of software testing. It significantly reduces the cost of fixing defects at the later stages of development. This is because it identifies the bugs or defects and fixes them at the early stages of development by checking each unit of the software product.

    2. Integration Testing

    Integration testing is the second level of software testing. Once the developers check each unit or component of the software product in isolation, they later integrate those units and test them as a whole. The primary purpose of integration testing is to identify defects when various software modules interact with each other after integration. Like unit testing, either developer or testers will perform integration testing. It entirely depends on an organization. Moreover, the primary focus of this type of testing is to make sure that the data flow between the software modules is intact.

    3. User Acceptance Testing

    As its name suggests, end-users or clients are responsible for performing user acceptance testing. A small group of real users or a client checks the software product to make sure it behaves as intended and meets all the business requirements before making it live to all the users. Since user acceptance testing involves end-users, we refer to it as end-user testing. It is the last type of testing that a software product undergoes after system and regression testing.

    4. Regression Testing

    Regression testing ensures that the software product functions as expected even after changing its source code. It makes sure that any new feature introduced in the software product does not affect its existing functionalities. In other words, it makes sure that the old code still works as expected, regardless of the latest changes made to it. Whenever there is a requirement change, we need to change the source code accordingly. Therefore, it becomes essential to test that modified source code. This is where regression testing comes into the picture. Moreover, regression testing is used after the developers fix defects and performance issues.

    5. Smoke Testing

    Some testing is a type of software testing that checks whether the software product's deployed build is stable or not. It confirms the quality assurance team to proceed with that build for the testing process. As we check whether the build of the software product is testable or not, we refer to smoke testing as build verification testing. In addition, it is also referred to as confidence testing. Smoke testing checks whether the significant and core features of the software product function well or not. Also, it ensures that there are no showstoppers in the build under test. In a nutshell, smoke testing ensures that the software product is ready for testing.

    6. Sanity Testing

    Sanity testing is the subset of regression testing, which ensures that any changes to the code do not affect the existing functionalities of the software product. During sanity testing, the testing team primarily focuses on checking the software product's functionality. Moreover, the testing team performs sanity testing only if the product passes smoke testing. If the sanity test fails, the testing team rejects the software product and saves further time and costs.

    Top 5 Functional Testing Tools

    A plethora of tools is available out there to carry out functional testing. The following are some popular functional testing tools :

    1. SoapUI

    SoapUI is an open-source web service testing tool for SOAP and REST web services. Along with scriptless functional testing, it also supports web service inspection, load testing, compliance testing, invoking, and development. This tool has an easy-to-use interface, which allows you to easily create and run functional, regression, and load tests. SoapUI provides complete test coverage with a single test environment, from SOAP and REST web services to databases and rich internet applications. Moreover, it comes with a commercial version called SoapUI Pro. This version has additional features that aim to improve the productivity of your software product.

    2. Selenium

    Selenium is a suite of tools and libraries that support browser automation. Using this tool, you can quickly automate web applications for testing. Not only does it automates testing but also mundane web-based administration tasks. There is no need to learn test scripting language to write functional tests since Selenium provides a playback tool called Selenium IDE. This IDE has its test domain-specific language called Selenese and allows you to write tests in various programming languages, including Java, Python, PHP, Perl, and Scala. Along with IDE, Selenium provides two other major tools: Selenium Grid and Selenium WebDriver. Selenium WebDriver enables you to create browser-based regression automation tests. On the other hand, Selenium Grid lets you run WebDriver scripts on multiple remote machines.

    3. Watir

    Watir stands for Web Application Testing in Ruby. It belongs to the family of Ruby libraries. It is an open-source tool for automating web browser testing. Moreover, Watir consists of three small projects: Watir-classic, Watir-webdriver, and Watirspec. Watir-classic leverages Ruby's OLE (Object Linking and Embedding) capabilities and directly operates the browser rather than simulating a browser. Watir-webdriver is the advanced version of Watir API, which is based on Selenium. Also, Watirspec is an executable specification of Watir API.

    4. Cucumber

    Cucumber is an open-source and commercially available testing tool that supports behavior-driven development. This tool allows you to write clean and readable tests that anyone without technical knowledge can understand. It runs automated acceptance tests developed in a behavior-driven development style. Moreover, Cucumber has its ordinary language parser called Gherkin. Gherkin is a language for writing test cases in Cucumber. It allows users to specify the behavior of the software product in a logical language that customers can easily understand.

    5. Ranorex

    Ranorex is a GUI test automation tool. It is easy to use and supports GUI testing of desktop, web, and mobile applications. You develop automated test modules in Ranorex using standard programming languages, such as VB.NET and C#. With Ranorex, you get the Ranorex Recorder that records the user's interaction with web and desktop applications and creates maintainable test scripts. You can further edit those scripts using the Ranorex Studio action editor. In addition, these scripts are available in C# and VB.NET. Ranorex also provides a proprietary technology called RanoreXPath, which supports GUI object recognition and GUI elements filtration.


    Functional testing is software testing that checks the software product against the functional requirements. It ensures that each function of the product works as intended. In another way, this type of testing validates the software product for its functionalities. In this article, we've gone through features, benefits, drawbacks, and different types of tools for functional testing. If you have any doubts or queries, share them with us by posting a comment below.

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    Non-functional testing implies testing the software product against non-functional requirements. It focuses on checking the non-functional aspects of the software products, such as performance and reliability. The primary objective of this type of testing is to ensure that the software product is reliable, usable, and maintainable.

    Ad-hoc testing, also known as random testing, is a type of testing that does not involve any proper planning and documentation. Also, there are no test cases and test designs. Testers carry out Ad-hoc testing randomly to identify bugs or defects in the software product.

    Both alpha and beta testing are types of user acceptance testing. Alpha testing involves identifying bugs or defects in the software product before making it live to end-users. On the other hand, best testing is a type of testing where real users of the software product test it for its reliability, security, and robustness.

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