Which of the following is NOT an example of non-functional testing?

Non-functional testing focuses on aspects of software that are not related to specific functionalities or behaviors of the system but instead assess criteria such as usability, performance, security, and reliability. Each of these criteria evaluates qualities of the software that affect the user's experience or the system's operation but do not pertain to what the software does in terms of functional capabilities.

Usability, for example, tests how easy and intuitive the software is for users. Maintainability examines how easily the software can be modified, which includes updating functionalities or fixing defects without introducing new bugs. Performance testing checks how the software behaves under various load conditions, measuring factors such as response time and throughput.

Functional requirements, however, define specific behaviors or functions the software must perform—essentially, what the software is supposed to do. Thus, they are not part of non-functional testing but rather the basis for functional testing, which ensures that these defined functionalities are working as expected. Understanding this distinction is crucial, as it helps clarify the purpose of different types of testing in software development and quality assurance.