Which testing type ensures that existing functionality is not adversely affected by new changes?

Regression testing is the testing type that specifically focuses on verifying that existing functionality remains intact after changes have been made, such as new features or fixes. It involves re-running previously conducted tests to ensure that previously working areas of the software behave as expected after any modifications.

This type of testing is crucial in agile environments, where changes occur frequently and rapidly. By identifying any unintended consequences of these changes, regression testing helps maintain the quality and stability of the software, ensuring that enhancements do not break established functionality.

In contrast, acceptance testing typically evaluates whether the system meets business requirements and is ready for delivery to end users. Functional testing focuses on verifying that specific functions of the application work as intended, but it does not specifically address the impact of changes on existing functionalities. Smoke testing serves as a preliminary check to see if the basic functionalities of the application are working, but it does not replace the thoroughness of regression testing when it comes to detecting any adverse effects from new changes.