What is the primary purpose of regression testing?

The primary purpose of regression testing is to ensure that changes made to the software, such as bug fixes or enhancements, do not introduce new issues or negatively impact existing functionality. After a defect is fixed or a new feature is added, regression testing is performed on the previously tested areas of the software to verify that everything continues to work as intended.

This process is crucial because even small changes in one part of the code can inadvertently affect other parts, leading to unexpected behavior or re-emergence of old defects. By systematically retesting the established functionalities, regression testing provides confidence that the software remains stable and reliable after changes have been made.

The other options focus on specific aspects of testing but do not capture the broader scope of regression testing. For instance, checking whether a specific defect has been fixed is part of the debugging process and may not reflect the overall stability of the application. Similarly, running new tests is typically associated with exploratory testing or validation of new features rather than assessing the impact of existing features. Lastly, isolating problems is a debugging task that is separate from the purpose of regression testing, which is more focused on overall software integrity.