Regressiontesting (rarely, non-regressiontesting) is re-running functional and non-functional tests to ensure that previously developed and tested software still performs after a change. If not, that would be called a regression.
<programming> Part of the test phase of software development
where, as new modules are integrated into the system and the
added functionality is tested, previously tested functionality
is re-tested to assure that no new module has corrupted the
system.
[Bennatan, E.M., "Software Project Management", 2nd edition,
McGraw-Hill International, 1992].
(1995-12-04)
Software regression
SOFTWARE BUG THAT BREAKS PREVIOUSLY WORKING FUNCTIONALITY
A software regression is a type of software bug where a feature that has worked before stops working. This may happen after changes are applied to the software's source code, including the addition of new features and bug fixes.