Functional Testing vs Non-functional Testing


Functional testing and non-functional testing are two different ways to test an application. These tests validate the functionalities of a software application. They also examine the performance, reliability, and usability of the said application. The main difference between these two types of tests lies in what they test for.

Functionality involves testing for correct functionality, whereas non-functional aspects include things like reliability and performance. This article will explore functional and non-functional testing, and then they will be compared to some common industry parameters. 

Functional Testing

Functional testing is also referred to as black-box testing. It ensures that all parts of the system work properly and nothing is missing or broken. The purpose of functional testing is to check whether the product works as intended, or whether any bugs in it need to be fixed before going live with the production release. Functional testers will test each feature individually and ensure that they work correctly before moving on to another feature.

Types of Functional Testing

There are two types of functional testing: unit testing and system testing.

Unit Testing

Unit tests verify only a single piece of code at a time. For example, if you’re writing a class that represents a person’s age in years, then writing a unit test for that class would be sufficient to verify that it works as expected. Unit testing typically focuses on one specific feature or behavior and runs quickly because they only need to test one function at a time.

System Testing

System tests verify a complete system by running all non-dependent modules and components together. For example, these tests might check whether all parts of an application are working properly together as they should.

Quality Control
Image: Vaeenma / Depositphotos

Non-Functional Testing

Non-functional testing is one of the most important types of testing for software developers because it ensures that a product meets all its functional requirements and does not contain any bugs or issues that could break down during production use once released into the wild. Non-functional testers will test each feature individually and make sure that it meets all its objectives before moving on to another feature

Types of Non-Functional Testing

There are three main types of non-functional testing:

Customer experience testing

The goal is to determine if the product works as expected, meets user needs, and is easy to use. This type of testing will help you determine if users are satisfied with the product. The focus here is on usability and not functionality.

Usability testing

This type of testing looks at how people interact with your product. It involves looking at how users navigate through various screens and use various features to answer questions like: “Does it work?” or “Is it easy to use?”

Performance testing

This type of testing focuses on measuring how well your application performs under certain conditions (e.g., high load). It involves running tests that measure response time, throughput, error rates, and more.

Parameters to compare Functional and Non-functional testing


Objectives are the outcomes of the test. Objectives are what we want to test. The objective of functional testing is to make sure that the software meets the requirements and specifications. The objective of non-functional testing is to analyze the software’s performance.

The objective of functional testing is to ensure that the product or service functions as intended. The objective of non-functional testing is to ensure that the product or service functions correctly.

Area of focus

Functional testing is performed to ensure that the application meets its functional requirements. The focus of this type of testing is on the user interface and the business logic of an application.

Non-functional testing is focused on ensuring that the application meets its non-functional requirements, such as security and performance. The focus of this type of testing is on ensuring that applications meet their specifications under various conditions, such as environmental or load conditions.

Ease of use 

Functional testing is more difficult than non-functional testing. Non-functional testing requires precise software application and it is easier to apply. Functional testing requires precise knowledge of the inner working of a program, which is not so easy to understand.

Functional testing can be done in an automated way as compared to non-functional testing, but if you want to check for bugs in your program you will need to write some code first. A bug hunter must know how his program works, but he also needs to test and debug it before it can be used by others.

Non-functional tests, on the other hand, are more complex to create and execute. You have to do some more work to understand what’s going on in your application, and you have to run them frequently so that you can catch regressions when they happen.


Functional testing is a type of software testing that checks the interaction between the user and the software. It is used to ensure that a program works as expected and does what it is supposed to do.

Non-functional testing is a type of software testing that checks the functionality of a product without regard to its user interface or inter-operability with other software products. Non-functional tests focus on how well the system meets its requirements, rather than how well it looks or feels to users.


Execution is the process of putting your test into action. Execution is defined as “the activity of using the software as it was intended to be used.” In functional testing, we execute the system to produce a result that is expected by the functional requirement. In non-functional testing, we execute the system to produce unexpected results that may violate a business rule or exception.


In conclusion, functional and non-functional testing should be used in tandem by software development teams. Given the state of modern software applications, the use of automated functional testing is rising and the importance of good testing automation can never be understated. Non-functional testing, on the other hand, will continue to play an important role in software development.

YouTube: Software Testing Tutorial #22 – Functional Testing vs Non-Functional Testing

Photo credit: The feature image has been done by Hay Dmitriy. The graphic about quality control has been done by Vaeenma.

This guest article has been submitted by Joy Anderson. While we appreciate guest contributions, it's important to note that the views expressed by the author are not necessarily reflective of those held by TechAcute.

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