Overview of Regression Testing and its objectives.

Regression testing is an important part of the software development life cycle. regression means going back. If any kind of modification is done in software, testing needs to be done to ensure that it works as specified and that it has not negatively impacted any functionality that it offered previously.
Common methods of regression testing include re-running previously run tests and checking whether previously fixed faults have re-emerged.

The objectives of regression testing are :
- To identify uncovered and unexpected defects.
- To ensure that changes or additions in the code are safe & are not liable to break the existing functionality of the application.
- To ensure and track the quality of its output.
- The changes to the software application have not introduced any new bugs.

Regression testing is necessary when there is a change made to an existing tested software. Each change implies more regression testing needs to be done to ensure that the system meets the project goals.
Regression testing can become cost effective if the test cases are automated the test cases may be executed using scripts after each change is introduced in the system. Also, teams do not execute all the test cases during the regression testing. They test only what they decide is relevant.

In short, regression testing means rerunning tests of things that used to work to make sure that a change didn't break something else. The set of tests used is called the Regression Test Set. It's enormously helpful when you change an application, change the environment, and during integration of pieces.
Regression testing is a simple concept, but it needs to be done just right to work in the real world.