What type of Testing checks if each program performs as expected?

Unit testing is focused on verifying that individual components or modules of a program function as intended. Developers typically conduct these tests to ensure that each unit, or smallest testable part of an application, works correctly and meets its specified requirements. By isolating each part of the program and testing its behavior, unit testing helps to identify bugs at an early stage of development, thus ensuring that each component performs as expected before they are integrated with other parts of the system.

This method is essential in establishing a strong foundation for the code, as it allows for quick identification and resolution of issues that can arise from changes or new additions to the codebase. The goal is not only to confirm that each unit operates correctly in isolation but also to ensure that it will integrate smoothly with other parts of the program during later testing stages.