Difference between Functional Testing and Non-Functional Testing

When the Software Requirement Specification is written all the functional and non-functional requirements are stated. The field of gathering requirements is known as Requirement Engineering.  Before delivering the software to the user or client both functional and non-functional requirements are tested. The process of testing those attributes which are stated in the software requirement specification is called testing process.

Functional Testing

Functional testing is testing of the features of the software that are necessary for software to work. In this type of testing all the functionalities which are demanded by the user are tested. And if the software is failed to meet the functional requirements than the software will fail and is rejected by the client. And all the resources are wasted. In functional testing there are two main categories which are known as Black Box Testing and White Box testing.

Non-functional Testing

Non-functional requirements are related with the behavior of the system. It is difficult to get the non-functional requirements from user because they are unaware about the non-functional requirements. Non-functional testing includes the testing of load, performance, reliability, scalability and usability testing. Different metrics have been defined to measure the behavior of the software.

Functional Testing VS Non-Functional Testing

Functions to be tested:

In functional testing the functionalities are tested. In this testing the basic features which are stated by the user.

In non-functional testing the response of the system is tested. That how much is taken by the system responds to the queries of user.

Performance time:

Functional testing is mostly performed before non-functional testing. It is performed by the testing team.

Non-functional testing is performed usually after the functional testing is done. And it is done by quality assurance team.

Elicitation:

Functional requirements are easily stated by the user as the user or client is aware about the functional requirements.

Non-functional testing is not easily explained by the user. Requirement engineer is supposed to ask such questions through which the non-functional requirements are explained.

Examples:

To test the login module that it is working according to the requirements is called functional testing.

The testing of security of the login module is called as non-functional testing.

Importance:

In most organizations functional requirements are given much importance. But non-functional requirements are ignored. This shows they are given more important than non-functional.

Non-functional requirements are given due importance in large organizations. They are less important than functional requirements.

Basis of testing:

The basis of functional requirements is user necessities.

The basis of non-functional requirements is user expectancy.

Validation:

Functional testing is done for validation of software actions.

Non-functional testing is done to validate the performance of the software.

Main Concerns:

Functional testing is performed to check that whether the system meets the productions requirements.

Non-functional testing is done for checking the client expectations.

Types:

The sub-types of functional testing are unit testing, integration testing, system testing, user acceptance testing and regression testing.

Performance tests, load testing, stress testing, reliability testing, size testing, usability testing, portability and scalability testing.

Conclusion

Functional and non-functional testing has their own importance. Both of them are vital for the success of software. If the software is failed to meet the functional or non-functional requirements it will eventually fails.