Which of the following testing methods tests the system efficiency by systematically selecting the suitable and minimum set of tests that are required to effectively cover the affected changes?

Unit testing tests individual components or modules of the software in isolation, not the overall system efficiency after changes.

Integration testing verifies the interfaces between different modules or components, not specifically focusing on changes impacting existing functionalities.

Acceptance testing is conducted to determine if the requirements of a specification or contract are met, typically performed by end-users, not focused on specific changes.

Regression testing is a type of software testing that aims to confirm that recent program or code changes have not adversely affected existing features. It involves re-running previously passed tests to ensure that the new changes haven't introduced new defects or reactivated old ones, often focusing on a minimum set of tests to efficiently cover the affected areas.