Why should regression testing be executed after changes if impact analysis indicates significant effect on the system?

Conducting regression testing after changes is essential primarily to ensure that the system continues to function as expected, without any new issues arising as a result of those changes. When significant impact is indicated by the impact analysis, this suggests that the changes could potentially affect various parts of the system or functionalities.

Regression testing involves re-running previously completed tests to verify that the existing features and functionalities work as they did before, thereby confirming that the changes made have not inadvertently introduced new defects. This process acts as a safeguard that reinforces the reliability and quality of the system following modifications.

Other options touch upon important aspects of software quality and maintenance, but they do not directly capture the primary focus of regression testing in the context of significant changes. For example, ensuring no unauthorized changes have been made is more aligned with security testing rather than regression, while assessing the scope of maintenance and identifying maintainability issues pertain to specific maintenance tasks rather than the overall verification of system functionality post-modification.