Difference between Functional and Non-functional Testing

Testing is the most important stage in the process of delivery of any application or software, as it not only validates the quality of an application but also provides an opportunity to the developer to improve its product.

Every application is developed as per the requirements of a customer/client. So, on the basis of testing the functionality of an application based on these requirements and testing the usability and performance, we can distinguish between Functional and Non-functional Testing.

Read this article to learn more about functional and non-functional testing and how they are different from each other.

What is Functional Testing?

Functional testing is a type of testing in which the basic functionality, operations and actions of the application/software is tested on the basis of the requirements provided by the client.

The objective of functional testing is to test each feature of an application by providing sufficient data and comparing the results. Functional testing is mainly concerned with the black-box testing and it is unconcerned with the source code of the application.

Functional testing tests the software program for user interface, APIs, database, security, client/server connection, and many other features. Functional testing may be performed automatically or manually.

Functional Testing Procedure

The following steps are to be followed for performing functional testing −

  • Determine the required functionality of the software or application.

  • Recognize the test input of test data based on the requirements.

  • Calculate the predicted outcomes by using the test input data.

  • Execute the test cases.

  • Compare the real and predicted results.

What is Non-Functional Testing?

Non-Functional testing is a type of testing in which the performance or usability and behavior of a software or application is tested under different circumstances. Non-functional testing is a software testing process that examines the non-functional attributes like productivity, compatibility, functionality, etc. of a software application.

The primary objective of non-functional testing is to assess the preparation of a system depending upon the non-functional conditions which are not covered by functional testing. An example of a non-functional testing is to check how many users would sign in to a program at the same time. Non-functional testing is essential to keep the specifications as the topmost priority.

Now, let us discuss the differences between functional testing and non-functional testing in detail.

Difference between Functional and Non-Functional Testing

The following are the important differences between Functional Testing and Non-Functional Testing −


Functional Testing

Non-Functional Testing


Functional testing is the testing in which the basic functionality, operations and actions of the application/software on the basis of requirements provided is done.

Non-Functional testing is the testing in which the performance or usability and behavior of software/application is done under different circumstances.

Nature of testing

As name states Functional testing does the functional verification of application process in which the requirement and corresponding written code has been verified so nature of functional testing is business requirement testing.

Non-Functional testing does the behavior validation and verification process which examines the expected behavior of the application based on dynamic inputs provided to the application so nature of non-functional testing is performance testing.

Testing target

As mentioned above, Functional testing targets the requirements of customer.

Non-Functional testing targets the expectations of customer.


For Functional testing, a check-list of application process and documentation is required.

For Non-Functional testing, performance test cases with different scenarios for execution have to be developed.

Stage of testing

Functional testing generally gets performed before compilation of code.

Non-Functional testing is mostly performed after compilation of code.

Cost to Company

In Functional testing, the cost of finding defects and fixing is less, also return on investment will be high as this testing is done at an early stage.

In case of Non-Functional testing, the cost of finding and fixing defects is high and also the return on investment will be low as this process takes place after the development phase


The most significant difference that you should note here is that functional testing does the functional verification of an application process, whereas non-functional testing does the behavior validation and verification process.

Updated on: 21-Feb-2023

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