What testing focuses on the internal workings of a software application?

White-box testing, also known as clear-box, glass-box, or structural testing, emphasizes the internal logic, structure, and implementation of the software application. Testers who perform white-box testing require knowledge of the code and its architecture, allowing them to design test cases that explore the internal pathways and conditions within the system. This type of testing helps identify areas for improvement, such as optimizing algorithms, checking control flow, and ensuring that all possible paths in the code are tested.

In contrast, other testing types like black-box testing focus solely on the software's outputs based on various inputs without any knowledge of the internal mechanics, assessing functionality against requirements. Integration testing concentrates on examining the interfaces and interactions between integrated components, while system testing evaluates the complete and integrated software product to ensure it meets specified requirements. Each of these methods serves a distinct purpose, but white-box testing's focus on internal workings sets it apart, making it the definitive choice for this question.