What type of testing assesses attributes unrelated to functionality, such as usability and reliability?

Non-functional testing is specifically designed to evaluate aspects of a system that do not relate directly to specific behaviors or functions, but rather to the quality attributes of the system as a whole. This type of testing investigates how well a system performs certain tasks and how it behaves under various conditions, focusing on performance, usability, reliability, security, and other characteristics that contribute to the user experience and system performance.

For instance, in non-functional testing, usability testing might assess how easy and intuitive a user interface is to navigate, while reliability testing would explore how consistently the system functions over time without failure. These attributes are crucial for understanding the overall quality and user satisfaction of the software, making non-functional testing an essential part of the testing lifecycle.

In contrast, functional testing specifically validates that the software operates according to requirements, regression testing focuses on ensuring that new code changes do not adversely affect existing functionality, and acceptance testing is concerned with confirming that the system meets the agreed-upon requirements and is ready for delivery to the end user. Each of these areas, while important, does not center on the non-functional attributes being assessed in the correct answer.