What is black box/white box testing

Black-box and white-box are test design methods. Black-box test designtreats the system as a "black-box", so it doesn't explicitly useknowledge of the internal structure. Black-box test design is usuallydescribed as focusing on testing functional requirements. Synonyms forblack-box include: behavioral, functional, opaque-box, andclosed-box. White-box test design allows one to peek inside the "box",and it focuses specifically on using internal knowledge of the softwareto guide the selection of test data. Synonyms for white-box include:structural, glass-box and clear-box.

While black-box and white-box are terms that are still in popular use,many people prefer the terms "behavioral" and "structural". Behavioraltest design is slightly different from black-box test design becausethe use of internal knowledge isn't strictly forbidden, but it's stilldiscouraged. In practice, it hasn't proven useful to use a single testdesign method. One has to use a mixture of different methods so thatthey aren't hindered by the limitations of a particular one. Some callthis "gray-box" or "translucent-box" test design, but others wish we'dstop talking about boxes altogether.

It is important to understand that these methods are used during thetest design phase, and their influence is hard to see in the tests oncethey're implemented. Note that any level of testing (unit testing,system testing, etc.) can use any test design methods. Unit testing isusually associated with structural test design, but this is becausetesters usually don't have well-defined requirements at the unit levelto validate.