Define Black box testing

Black box testing Black-box test design care for the system as a "black-box", so it doesn't explicitly use knowledge of the internal structure. It takes an external perspective of the test object to derive test cases. These tests can be functional or non-functional, though typically functional. The test designer selects valid and invalid input and verifies the correct output. There is no knowledge of the test object's internal structure. This means of test design is applicable to all levels of software testing: unit, functional testing, integration, system and acceptance.