At what levels can white-box testing be applied?

• A. Unit, system, and acceptance
• B. Unit, integration, and system
• C. Module, integration, and performance
• D. Design, development, and deployment

Answer: (B)

White-box testing uses knowledge of the internal code and logic to verify correctness at different levels of granularity. It can be applied at unit, integration, and system levels.

In unit testing you target individual components or functions, exercising internal branches and paths to ensure each piece behaves correctly in isolation. In integration testing you examine how modules interact, focusing on interfaces and data flow between components, still leveraging knowledge of internal structures to validate correct cooperation. In system testing you verify the whole, integrated product, and white-box insight helps check how internal components drive overall behavior and meet requirements.

Acceptance testing is typically black-box, looking from the user perspective without internal details. Performance testing focuses on speed and efficiency and isn’t a separate white-box level, and design, development, and deployment are phases, not testing levels.