Black box testing essentially means that the testers don’t have access to the source code of the application. They are testing what the customer wants the application to do, not what the developer programmed it to do. Testers performing black box testing know only that information is put in, what to expect the application to return, but do not know how that information is processed or returned. The internal functioning is a “black box” to the tester. This kind of testing focuses on the software functionality instead of internal system processes. It is used to analyze requirements, high-level designs, and specifications. This kind of testing is sometimes referred to as functional testing or behavioral testing.

Strategies for black box testing include validating each requirement, performing boundary tests, equivalence partitioning, and using both valid and invalid input to return correct system responses. All possible combinations of user actions are generally tested in order to accurately simulate the end-user experience. The types of defects generally found in black box testing are incorrect/missing functions, interface errors, data errors, or access errors.

Many types of testing use black-box testing methods, such as functional testing, requirements testing, security testing, and performance testing. A big bonus with black box testing is that the test cases can be written as soon as requirements are finished, giving testers a jump start on the testing process.