What is unit testing in software development?

Unit testing is a critical aspect of software development that focuses on evaluating the smallest testable parts of an application, often referred to as "units." These units can be individual functions, methods, or classes within the codebase. The primary goal of unit testing is to ensure that each component behaves as expected in isolation, which helps identify bugs and issues at an early stage in the development process.

By performing unit tests, developers can verify that specific functionalities within the code return the correct outputs for given inputs, allowing for more efficient debugging and maintenance. This process also encourages developers to write modular code, making it easier to manage and scale over time.

The other options, while related to testing in the software development lifecycle, do not accurately describe unit testing. Testing system architecture involves evaluating the overall structure and design of the application, testing integration examines how different systems or components work together, and testing user interfaces focuses on the interaction between users and the application, rather than individual code components. Each of these activities serves a distinct purpose in the broader context of software quality assurance and does not reflect the specific focus of unit testing.