Which of the following is a common type of software testing?

Unit testing is a fundamental type of software testing that focuses on verifying individual components or functions of the software to ensure they work as intended. This type of testing is typically performed by the developers themselves and is aimed at catching bugs early in the development process, which can save time and resources later on. Unit testing involves testing the smallest parts of an application, such as functions, methods, or classes, to validate that each unit of the software performs as expected given a set of inputs.

Although performance testing, regression testing, and integration testing are also vital and common types of software testing, they serve different purposes. Performance testing evaluates how the system performs under specific conditions, regression testing ensures that new code changes do not adversely affect existing functionality, and integration testing verifies that various components of the system work together correctly. Each of these types of testing is important in its own right, but unit testing is particularly significant for catching issues at the most granular level early in the software development lifecycle.