Difference Between Functional and Non functional Testing

Difference Between Functional and Non functional Testing: Functional and Non functional Testing is a crucial part of the software development cycle. It’s important to understand what both mean and how they’re different from each other. Let’s dive in!

Functional Testing

Functional testing refers to the process of executing a program with the intent of finding bugs (also known as Software Defects) in it. It is used to determine if the application meets its requirements and specifications documents by testing all of its features with the intent of finding defects.

Functional Testing is basically tests done to validate the functionality of an application. Unlike Non-Functional Testing, Functional focuses on only one thing i.e., whether that particular feature works or not.

Basic things to remember :

Functional Testing is done at the end of each sprint. Its purpose is to verify that all features have been implemented and are working as expected. To facilitate this, a set of test cases should be defined for each feature before implementation begins. These test cases are then executed after implementation and any failures should be investigated and sorted out.

Functional Testing is also known as End to End Testing as it ensures that each feature works towards the intended outcomes. This test is an essential part of the development cycle, especially in Agile projects where testing focuses on finding bugs early in the software development lifecycle when they are easier to fix.

Functional Testing ensures that the application meets all requirements and conforms to standards. This test should be carried out in a non-production environment of the software product, so as not to interfere with its normal working.

Functional testing is based on the internal logic of an application i.e., it tests internal code paths, data responses, performance, and any other internal element of the application.

Non-functional Testing

Unlike Functional testing, Non-functional testing is a broad category of software tests that do not relate to the functionality of an application. Instead, it verifies any other requirement that the system under test may have like performance, scalability, reliability, etc and ensures that these requirements are being adhered to. Basically tests that are not related to the functionality of the application.

Non-functional testing is also known as Acceptance Testing as it determines whether the system meets the requirements set by users and other stakeholders. It makes sure that if all features work as expected and are meeting the client’s expectations.

The primary goal of non-functional testing is to find out whether the product meets its requirements, though functional testing may contribute to this also. It is essential that non-functional tests be carried out to prevent issues with the software once it has been released into production.

Non-Functional testing aims at finding defects outside of the application’s functional scope. It has many sub-types like Stress, Performance, and Security testing, etc are some main subtypes of Non-Functional Testing.

Difference Between Functional and Non functional Testing

Functional and Non functional Testing is one of the most common comparisons between these two paradigms.

Functional Testing can be considered a subset of Non-Functional Testing as it covers the only functional aspects of software and some others like performance, scalability, etc are considered “non-functional” because they do not pertain to functionality but rather other aspects like stability, reliability, etc.

Nevertheless, both functional and non-functional testing is equally important parts of the software development lifecycle and should be used for verifying quality as per the project requirements.

Functional Testing is a broader term that includes all types of tests that verify application/software’s functionality. Whereas Non-Functional Testing comprises all those tests that are not related to software application functionality.

Functional Testing

  • It is also known as End to End and White Box Testing.
  • Functional testing ensures that the application works according to the requirements set out for it, i.e., it verifies that each function achieves what it is supposed to achieve and operates in the way specified by its specifications.
  • It involves testing of internal logic of an application, data responses and performance. It tests all features work as specified in the requirement documents.
  • Functional testing must be carried out in conjunction with Non-Functional Testing as Functional testing alone cannot assure that the system is fit for its intended purpose.
  • It ensures that application is working as per requirements and it covers both positive and negative cases. This helps in detecting design flaws, coding errors, logic errors etc.
  • It is normally carried out by the developers or QA engineers.

Non-Functional Testing

  • It is also known as “Acceptance” testing. It ensures that the system meets the requirements set by users and other stakeholders.
  • Non-functional testing is not concerned with the internal logic of application but looks outside and examines how the product will perform, behave and work with other systems when it is in production.
  • Functional testing alone cannot assure that the system is fit for its intended purpose. Nonfunctional testing is required to ensure that the system meets performance, scalability, reliability and availability requirements.
  • Non-functional testing ensures that the application is capable of handling the peak loads, user authentication and various security threats that can be faced by application in production environment.
  • This type of testing is also required to make sure that customers can actually use the application. They need to be able to access it, navigate through its screens and links, enter appropriate information and receive appropriate responses.
  • Non-functional testing is very important as it emphasizes on non functional requirements that are vital for the successful deployment of an application.
  • It ensures that the system will work with others. This is especially important for an enterprise application where multiple systems need to interact and work together to provide an integrated whole.
  • Non-functional testing ensures that the product under test performs its tasks and functions as expected using such metrics of performance, scalability, reliability and availability as the customer requires.
  • Non-functional testing is considered to be more important than functional tests because its results are not easily quantifiable and they do not lend themselves readily to automation.
  • Non-functional tests check that application works as desired but it is up to the developer to create positive and negative test cases to check that the application performs as required.
  • Non-functional testing is a form of integration testing in which different parts of an application are combined and tested as a whole.


The objective of using both Functional and Non functional Testing is to explain the desired behavior of software applications. As they serve different objectives, there is no one can replace another.

Non Functional Testing helps in ensuring that the application meets certain performance levels which are required by the customer. Whereas  Functional Testing ensures that all features work as per requirements specified in requirement documents.

So these two types of testing are complementary to each other as none can replace the role of the other. Hope this blog helped you in understanding Functional and Non functional Testing, their importance, and advantages which ultimately lead to successful software delivery. Do let me know if you need any clarifications through the comment.

I love open-source technologies and am very passionate about software development. I like to share my knowledge with others, especially on technology that's why I have given all the examples as simple as possible to understand for beginners. All the code posted on my blog is developed, compiled, and tested in my development environment. If you find any mistakes or bugs, Please drop an email to softwaretestingo.com@gmail.com, or You can join me on Linkedin.

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