Black Box, often referred to as behavioral testing or external testing, is a form of software testing technique wherein no prior knowledge of the internal code structure, implementation specifics, or internal routes of an application is necessary. It focuses on the application's input and output and is entirely dependent on the specifications and requirements for the software.
Gray box testing, which combines black box and white box testing, is a software testing approach used to test an application while only having a general understanding of its core code. It searches for and identifies context-specific errors that the application's poor code structure has produced.
White Box testing examines a software's underlying structure, coding, and architecture in order to validate the input-output flow and improve the application's design, security, and utility. Testing of this kind is sometimes referred to as internal testing, clear box testing, open box testing, or glass box testing because testers can see the code.