What type of testing verifies that recent changes in a system haven't introduced new errors?

Regression testing is essential for ensuring that new changes, such as bug fixes, feature enhancements, or system updates, have not adversely affected the existing functionality of the software. This type of testing involves re-running previously completed tests to confirm that the software continues to perform as expected after modifications have been made.

By focusing on the areas of the application that might be impacted by recent changes, regression testing helps detect any unintended side effects or new defects that could arise from those changes. It is a critical step in the software development lifecycle that maintains software reliability and quality as it evolves.

In contrast, unit testing primarily focuses on individual components or functions in isolation, integration testing examines interactions between integrated units, and user acceptance testing involves validating the system with actual users based on requirements and business needs. While all these types of testing are important, regression testing specifically addresses the concern of new errors resulting from recent changes.