Which type of testing is focused on validating that changes in code do not negatively impact existing functionalities?

The focus of regression testing is to ensure that new code changes do not introduce defects or negatively affect the functionality of existing features within the software application. Essentially, after developers make modifications or add new features, regression tests are executed to confirm that the software still behaves as expected. This type of testing aims to catch issues that might arise from updates, ensuring the integrity of the software remains intact.

While unit testing concerns itself with testing individual components or functions in isolation, and performance testing evaluates the responsiveness, speed, scalability, and stability of the system under load, regression testing specifically targets the overall functionality after any changes are made to confirm that no existing functionality has been broken. Additionally, smoke testing is a preliminary check to see if the most crucial functions of the application work after a build, rather than a thorough validation of existing functionalities. Therefore, regression testing is the key methodology for confirming that existing capabilities are preserved throughout the development lifecycle.