Which statement best describes the purpose of non-functional testing?

The purpose of non-functional testing is indeed best described by measuring characteristics of a system that indicate how it performs its functions. Non-functional testing focuses on aspects such as performance, usability, reliability, and security, rather than the specific behaviors or functions of the software. This type of testing evaluates how well the system operates under various conditions and helps identify any potential bottlenecks or issues that could affect the user experience or system efficiency.

The correct answer highlights that non-functional testing is concerned with the attributes that enhance the overall functionality of the system, providing a holistic view of its performance capabilities. This is essential for understanding the quality and effectiveness of the system in real-world scenarios, as users often care as much about how well an application performs as they do about what functions it offers.

The other options focus on specific compliance standards, system reliability, and functional testing, which are critical but do not encompass the broader purpose of non-functional testing, which is centered around performance characteristics and user experience.