Regression testing - types - uses

Regression testing is any type of software testing which seeks to uncover regression bugs. Regression bugs occur whenever software functionality that previously worked as desired, stops working or no longer works in the same way that was previously planned. Typically regression bugs occur as an unintended consequence of program changes.

Common methods of regression testing include re-running previously run tests and checking whether previously fixed faults have re-emerged.Experience has shown that as software is developed, this kind of reemergence of faults is quite common. Sometimes it occurs because a fix gets lost through poor revision control practices (or simple human error in revision control), but often a fix for a problem will be "fragile" in that it fixes the problem in the narrow case
where it was first observed but not in more general cases which may arise over the lifetime of the software. Finally, it has often been the case that when some feature is redesigned, the same mistakes will be made in the redesign that were made in the original implementation of the feature.

Types of regression
· Local - changes introduce new bugs.
· Unmasked - changes unmask previously existing bugs.
· Remote - Changing one part breaks another part of the program. For example, Module A writes to a database. Module B reads from the database. If changes to what Module A writes to the database break Module B, it is remote regression.

There's another way to classify regression.
· New feature regression - changes to code that is new to release 1.1 break other code that is new to release 1.1.
· Existing feature regression - changes to code that is new to release 1.1 break code that existed in release 1.0.

Mitigating regression risk
· Complete test suite repetition
· Regression test automation (GUI, API, CLI)
· Partial test repetition based on traceability and analysis of technical and business risks
· Customer or user testing
oBeta - early release to both potential and current customers
oPilot - deploy to a subset of users
oParallel - users use both old and new systems simultaneously
· Use larger releases. Testing new functions often covers existing functions. The more new features in a release, the more "accidental" regression testing.
· Emergency patches - these patches are released immediately, and will be included in future maintenance releases.

Uses
Regression testing can be used not only for testing the correctness of a program, but it is also often used to track the quality of its output. For instance in the design

of a compiler, regression testing should track the code size, simulation time and compilation time of the test suite cases.