Date Added: May 2011
Regression testing is the activity of retesting a program so as to ensure that no new errors have been introduced into the previously tested code. However, this activity does not involve rerunning the entire test suite but selecting only a few test cases that exercise the changes. Suppose there is a program P and P' is it's modified version. The regression test suite so selected must be able to reveal the differences between P and P' that would help the developer discover errors caused by changes. More and more emphasis has been laid in identifying the regression test suites and ordering them.