OCUnit is a unit testing framework for Objective-C programming language. It is used by developers to create and run automated tests to ensure that their code works properly and reliably. OCUnit allows developers to write test cases that can be run with the Xcode IDE or from the command line, and provides tools for generating reports and analyzing test results. It is typically used in software development projects that use the Agile methodology, as it helps ensure the quality and reliability of the code as it is developed.