Final answer:
Usability testing is categorized as non-functional testing, evaluating the user-friendliness and satisfaction of an application rather than its specific functions.
Step-by-step explanation:
Usability testing is an example of non-functional testing. This type of testing involves assessing how easy it is for users to use the application and how user-friendly the application is. It does not test specific functions of the software; rather, it evaluates aspects such as user satisfaction, accessibility, and compliance with user requirements
In usability testing, the goal is to identify areas where users may have difficulties and to improve the overall user experience.