Which of the following types of software testing ensures that previously working functionality is still operational after changes?

Regression Testing focuses on verifying that new code changes, bug fixes, or feature additions have not adversely affected the existing functionality of the software. It is a critical step in maintaining software quality during iterative development. Automated tools like Selenium or JUnit are often used to conduct regression tests, ensuring efficiency and consistency. For example, after adding a new feature to an e-commerce application, regression testing ensures that existing functionalities, such as login and checkout, remain unaffected. This testing minimizes risks of breaking critical features and enhances user satisfaction. Why Other Options Are Incorrect :

1. Unit Testing : Verifies individual components or units of code but does not ensure the overall system's previous functionality remains intact.
2. Integration Testing : Focuses on verifying interactions between modules, not on previously working features.
3. User Acceptance Testing : Ensures that the software meets user requirements but does not focus on testing after changes.
4. Performance Testing : Measures software performance under load and stress, unrelated to functionality regression.