Regression Testing Technique :

Background	§ One segment of system is developed and thoroughly tested. § Another segment is changed which has disastrous effect on the tested segment. § The implemented change, new data or parameters have created change in the already tested segment.
Usage	§ All aspects of system remain functional after testing. § Change in one segment does not change the functionality of other segment.
Objectives	§ Determine – - system documents remain current - System test data and test conditions remain current. - Previously tested system functions properly without getting effected though changes are made in some other segment of application system.
How to Use	§ Test cases, which were used previously for the already tested segment is, re-run to ensure that the results of the segment tested currently and the results of same segment tested earlier are same. § Test automation is needed to carry out the test transactions (test condition execution) else the process is very time consuming and tedious. § In this case of testing cost/benefit should be carefully evaluated else the efforts spend on testing would be more and payback would be minimum.
When to use	§ When there is high risk that the new changes may effect the unchanged areas of application system. § In development process: Regression testing should be carried out after the pre-determined changes are incorporated in the application system. § In Maintenance phase : regression testing should be carried out if there is a high risk that loss may occur when the changes are made to the system
Example	§ Re-running of previously conducted tests to ensure that the unchanged portion of system functions properly. § Reviewing previously prepared system documents (manuals) to ensure that they do not get effected after changes are made to the application system. § Obtaining printout of data dictionary to ensure that the data elements reflect the changes being incorporated.
Disadvantage	§ Time consuming and tedious if test automation not done.