Regression testing is testing the module in which a bug was identified earlier along with the impacted areas to ensure that this fix has not introduced any further defects.

The purpose of regression testing is to ensure that previously detected and fixed issues really are fixed, they do not reappear, and new issues are not introduced into the program as a result of the changes made to fix the issues.

Regression testing also referred to as verification testing, is initiated after a programmer has attempted to fix a recognized problem or has added source code to a program that may have inadvertently introduced errors. It is a quality control measure to ensure that the newly modified code still complies with its specified requirements and that unmodified code has not been affected by the maintenance activity.

Regression Testing is in general a black box testing strategy where test case execution of previously written test cases, that has exposed bugs, is done to check whether previously fixed faults have reemerged. In a test suite, all the tests that has caused bug are written and are re-tested whenever changes are made to the program to fix any bug. But this is a tedious process as after every compilation it is difficult to go through the process of retesting all the test cases repeatedly. To make this process simpler regression testing is automated using some testing tools.

Typically regression testing should be performed on a daily basis. Once an issue in the defect Tracking database has been fixed it is reassigned back for final resolution. Now it can be either reopens the issue, if it has not been satisfactorily addressed, or close the issue if it has, indeed, been fixed.