Regression testing is testing that is carried out on previously tested features, right after any change is introduced to this feature. The purpose of regression testing is to ensure the newly introduced change has not broken the feature it is introduced to.
Regression testing is any type of software testing that seeks to uncover new software bugs, or regressions, in existing functional and non-functional areas of a system after changes, such as enhancements, patches or configuration changes, have been made to them.
The intent of regression testing is to ensure that a change such as those mentioned above has not introduced new faults. One of the main reasons for regression testing is to determine whether a change in one part of the software affects other parts of the software.
Common methods of regression testing include re-running previously-completed tests and checking whether program behavior has changed and whether previously-fixed faults have re-emerged. Regression testing can be used to test a system efficiently by systematically selecting the appropriate minimum set of tests needed to adequately cover a particular change.