What does unit testing primarily focus on?

Unit testing primarily focuses on testing each individual component or program in isolation to ensure that it performs as expected. By examining the smallest testable parts of an application, such as functions or methods, developers can identify and address issues at an early stage of development. This allows for a granular approach to validating code behavior, ensuring that each part of the software operates correctly before it is integrated with other components.

This focused testing helps pinpoint where errors exist in specific units of code, making it easier to diagnose problems and ensuring that the fundamental building blocks of an application function as intended. It provides a strong foundation for further testing processes such as integration testing, where these components work together, thereby improving the overall quality and reliability of the software.

Other options describe different testing contexts. Testing the system as a whole refers to system testing, which evaluates the entire application. Preparing for a series of tests relates to a testing strategy, and providing final certification pertains to acceptance testing, which assesses if the complete system meets business needs. Each of those focuses on broader testing scopes compared to the specificity of unit testing.