Regression testing is a type of software testing that verifies whether a change in the software does not introduce any new errors or issues and does not impact the existing functionality of the system. Regression testing is performed when a new feature is added, an existing feature is modified, or a bug is fixed in the software.

The purpose of regression testing is to ensure that the changes made to the software have not adversely affected the system’s existing functionality. Regression testing involves re-executing the existing test cases that cover the affected areas of the software to ensure that the changes have not caused any unintended side-effects.

Regression testing is essential because any change in the software can cause new defects or introduce unexpected behavior, which can have serious consequences if not caught early. Regression testing is usually automated because it can be time-consuming and repetitive to execute the same test cases manually after every change in the software. Automating regression testing ensures that the tests are executed consistently and with greater accuracy, which leads to more reliable test results.