Which testing approach focuses on the internal workings of an application?

The approach that concentrates on the internal workings of an application is white box testing. This method involves an understanding of the internal logic, structure, and implementation of the software being tested. Testers examine the code, algorithms, and control flows, allowing for the creation of test cases that evaluate the program's functioning at a granular level.

By focusing on the internal components, testers can identify hidden errors, assess the software's behavior under various scenarios, and ensure that all code paths are exercised. This level of scrutiny helps ensure the software's reliability and correctness, making it a crucial part of the overall testing strategy, especially for critical systems where the internal logic needs to be validated thoroughly.

In contrast, other testing approaches, such as black box testing, do not consider internal coding but rather examine outputs based on various inputs. User acceptance testing is aimed at ensuring the software meets user requirements and is acceptable for delivery. Performance testing assesses how a system performs under various conditions, focusing on speed, responsiveness, and stability rather than the internal code structure. Each method serves different purposes in the testing lifecycle, but white box testing specifically is distinct in its internal focus.