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.

[edit] 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
          o Beta - early release to both potential and current customers
          o Pilot - deploy to a subset of users
          o Parallel - 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.

[edit] 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.

[edit] Quotes

    * "Also as a consequence of the introduction of new bugs, program maintenance requires far more system testing per statement written than any other programming. Theoretically, after each fix one must run the entire batch of test cases previously run against the system, to ensure that it has not been damaged in an obscure way. In practice, such regression testing must indeed approximate this theoretical idea, and it is very costly." -- Fred Brooks, The Mythical Man Month (p 122)

[edit] See also

    * Quality control
    * Software development process
    * Unit testing
    * Smoke testing