What does 'unit testing' refer to?

Unit testing refers specifically to the practice of testing individual components or functions of a program in isolation. This approach allows developers to verify that each part of the code behaves as expected, ensuring that specific segments of code work correctly before they are integrated into a larger system. The focus is on the smallest units of code, typically functions or methods, which can be tested independently.

By focusing on these individual components, unit testing helps identify bugs or issues at an early stage of development, making it easier to locate the source of a problem. This practice also encourages better coding practices since developers aim to write code that is modular and easier to test. Therefore, the value of unit testing lies in its ability to ensure that each small part of an application functions correctly, reducing the chances of errors when those parts are combined.

In contrast, testing an entire application at once is more aligned with integration or system testing, rather than unit testing. Testing user interfaces focuses on the interaction between users and the application as a whole. Performance testing under load assesses how well the system performs under various conditions but does not target the functionality of individual components in isolation.