Black Box Testing

In black box testing we check the functionality of the software using different inputs. Internal coding of the software is not tested. The test designer selects valid and invalid input and determines the correct output. There is no knowledge of the test object's internal structure. The implementation details of the components are not known (or, at least, are ignored), and only externally observable behavior or functionality is tested. This method of test design is applicable to all levels of software testing: unit, integration, functional testing, system and acceptance.
Black box testing is sometimes also called as "Opaque Testing", "Functional/Behavioral Testing" and "Closed Box Testing".