Which type of testing focuses on the external behavior of software?

Black box testing focuses on the external behavior of software by evaluating its functionality against specified requirements without any consideration for the internal workings or structure of the application. Testers using this approach assess the software's outputs based on various inputs and check whether the software behaves as expected. This type of testing is particularly useful for validating that the software meets its functional requirements and for identifying any discrepancies between expected and actual outcomes.

In essence, black box testing emphasizes what the software does rather than how it does it, making it suitable for user acceptance testing and other situations where the end user's perspective is essential. This contrasts with other testing methods where the internal logic, design, and code are scrutinized, as in white box testing, which looks at the internal structure and pathways of the code. Grey box testing combines elements of both black and white box testing, while static testing involves reviewing code or documents without executing them to find defects early in the development process. Each of these approaches serves distinct purposes, but black box testing is specifically aligned with examining the external behavior of software.