Difference between Functional Testing and Non-Functional Testing
Published: 2023-09-15 17:55:15

Functional testing
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Functional testing focuses on the software functional requirements rather than its internal implementation. A functional requirement refers to required behavior in the system. Functional testing validates the software against the functional requirements or the specification, ignoring the non-functional attributes such as performance, usability, and reliability. It is a form of black-box testing in which the basic functionality, operations and actions of the application on the basis of requirements provided is done. 

Functional testing aims to address these 2 questions: Does it solve its intended users' problems? Does the software fulfill its functional requirements?


Non-functional testing
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Non-functional testing refer to an attribute or quality of the system explicitly requested by the client. These include performance, security, scalability, and usability. Non-functional testing comes after functional testing. It tests the general characteristics unrelated to the functional requirements of the software. Non-functional testing ensures that the software is secure, scalable, high-performance, and won't crash under heavy load. Non-Functional testing is the testing in which the performance or usability and behavior of application is done under different circumstances.


Other Differences between Functional testing and Non-functional testing:
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Nature of testing: 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: Functional testing targets the requirements of customer. Non-Functional testing targets the expectations of customer.

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

Common to both are Verification and Validation
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Verification: It is defined as a process that involves analyzing the documents. This process verifies whether the software conforms to specifications or not.  Its ultimate goal is to ensure the quality of software products, design, architecture, etc.  It checks whether the software meets the specification or not. It is a type of static testing.There is no requirement of executing the code. This process is performed by the QA team to make sure that the software is built as per the specifications in the SRS document.Reviews, walkthroughs, inspections, and desk-checking are some methods that can be used in verification. It identifies the bugs or errors early in the development process. It is performed before the validation process.

Validation: It is defined as a process that involves dynamic testing of software products by running it. This process validates whether we are building the right software that meets that customer requirement or not. It involves various activities like system testing, integration testing, user acceptance testing, and unit testing.It checks whether the specification captures the customer’s needs or not. There is a requirement for executing the code.This process is performed with the involvement of the testing team. Black box testing, white box testing, and non-functional testing are some methods that can be used during validation. It can identify the bugs or errors that the verification process cannot catch.It is performed after the verification process.