Functional vs Non-Functional Testing

Krisnawan Hartanto
3 min readJan 31, 2023

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In this article, I will talk about functional and non-functional testing, and how both of them complement each other.

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Functional vs non-functional testing

What is?

What is Functional Testing

Functional testing is a type of software testing that focuses on the user’s experience with the application. It’s usually performed by manually executing the application to determine whether or not it meets the functional requirements.

Functional testing is performed using the functional specification provided by the client and verifies the system against the functional requirements. Functional testing is executed first, using manual testing or automation tools.

Business requirements are the inputs to functional testing. Functional testers ensure that products work as intended by verifying that they meet all business requirements as defined in specifications and user stories.

“Functional testing is testing that the software works as it should. Testing that the design and requirement specifications have been met. We test the application from the perspective of the end-user.” ~ Ozan İlhan

What is Non-Functional Testing

Non-functional testing is the process of performing a test against a product, software, or system, for its non-functional requirements.

Non-functional tests are often performed after functional testing and can include things like performance, reliability, scalability, and other non-functional aspects of the system. It can give insights into how well the product works. Using the right tools will be effective for this testing.

Performance parameters like speed and scalability are goals for non-functional testing. Performance parameters also influence user experience. For example, if a website takes 1 min to load then users might not find it acceptable and leave it immediately or they might wait for a while before leaving only to find out that their site was down because of heavy traffic or something else but they had no way to know that until they tried to use it. This type of information is important for designers so they know what kind of performance they need in their products.

“Non-Functional testing is concerned with the non-functional requirements and is designed specifically to evaluate the readiness of a system according to the various criteria which are not covered by functional testing.”~ Ozan İlhan

Testing Type

Examples of Functional testing are

  • Unit Testing
  • Smoke Testing
  • Sanity Testing
  • Integration Testing
  • White box testing
  • Black Box testing
  • User Acceptance testing
  • Regression Testing

Examples of Non-functional testing are

  • Performance Testing
  • Load Testing
  • Volume Testing
  • Stress Testing
  • Security Testing
  • Installation Testing
  • Penetration Testing
  • Compatibility Testing
  • Migration Testing

Conclusion

Even though both types of testing serve different purposes, it can be said that both types of testing are complementing each other and can be integral parts of the whole software testing activities. Functional testing focuses the testing on the functional requirement of the software. Meanwhile, non-functional testing focuses on the different requirements of the software like performance, reliability, scalability, and other non-functional aspects of the system.

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