Which statement BEST describes non-functional testing?

Non-functional testing focuses on the attributes of a system that are not related to specific functionalities. This type of testing evaluates the performance, usability, reliability, and other quality attributes that contribute to the overall user experience and effectiveness of the system. By concentrating on these non-functional aspects, it helps ensure that the system not only performs the required tasks but does so under various conditions and meets user expectations.

The significance of identifying system attributes like usability, reliability, and maintainability is clear. Usability pertains to how easy and intuitive the system is for users, reliability indicates the system's ability to function correctly under predefined conditions, and maintainability refers to how easily the software can be updated or modified in the future. This category of testing is critical in software development because even a perfectly functioning application can fail if it is not user-friendly or reliable.

The other options describe different aspects of testing processes that do not encapsulate the essence of non-functional testing. For example, verifying whether a system meets specified requirements relates more to functional testing, compliance with coding standards falls under code reviews or static code analysis, and testing without reference to internal structure aligns with black-box testing, which may still involve functional attributes rather than focusing solely on non-functional criteria.