In which type of testing does a tester know the internal details of the software being tested?

White box testing involves the tester having full knowledge of the internal workings of the software being tested, including the code, architecture, and infrastructure. This type of testing allows for a comprehensive assessment of the software's internal logic and flow, enabling the tester to create specific test cases that target specific functions, branches, loops, and paths within the application.

This depth of understanding makes it possible to identify vulnerabilities and bugs that might not be apparent through other testing methods, as the tester can directly analyze how the application processes data and handles various conditions. The insight gained from white box testing is crucial for identifying security flaws and ensuring that the application adheres to design specifications and security policies, making it a vital component of a robust security assessment strategy.

Other testing types, such as black box testing, do not provide insight into the internal workings of the software; testers only interact with the software's inputs and outputs. Gray box testing combines aspects of both white and black box testing, while exploratory testing relies on tester intuition and experience without a structured approach to test coverage.