Regression Testing

The selective retesting of a software system that has been modified to ensure that any bugs have been fixed and that no other previously working functions have failed as a result of the reparations and that newly added features have not created problems with previous versions of the software. Also referred to as verification testing, regression testing is initiated after a programmer has attempted to fix a recognized problem or has added source code to a program that may have inadvertently introduced errors. It is a quality control measure to ensure that the newly modified code still complies with its specified requirements and that unmodified code has not been affected by the maintenance activity.

 

Regression testing is the process of testing changes to computer programs to make sure that the older programming still works with the new changes. Regression testing is a normal part of the program development process and, in larger companies, is done by code testing specialists. Test department coders develop code test scenarios and exercises that will test new units of code after they have been written. These test cases form what becomes the test bucket. Before a new version of a software product is released, the old test cases are run against the new version to make sure that all the old capabilities still work. The reason they might not work is because changing or adding new code to a program can easily introduce errors into code that is not intended to be changed.

 

 Like confirmation testing or Retesting, regression testing involves executing test cases that have been executed before. The difference is that, for regression testing, the test cases probably passed the last time they were executed (compare this with the test cases executed in confirmation testing - they failed the last time).

The term 'regression testing' is something of a misnomer. It would be better if it were called 'anti-regression' testing because we are executing tests with the intent of checking that the system has not regressed (that is, it does not now have more defects in it as a result of some change). More specifically, the purpose of regression testing is to verify that modifications in the software or the environment have not caused unintended adverse side effects and that the system still meets its requirements.

             

 It is common for organizations to have what is usually called a regression test suite or regression test pack. This is a set of test cases that is specifically used for regression testing. They are designed to collectively exercise most functions (certainly the most important ones) in a system but not test any one in detail. It is appropriate to have a regression test suite at every level of testing (component testing, integration testing, system testing, etc.). All of the test cases in a regression test suite would be executed every time a new version of software is produced and this makes them ideal candidates for automation. If the regression test suite is very large it may be more appropriate to select a subset for execution.

 

Regression tests are executed whenever the software changes, either as a result of fixes or new or changed functionality. It is also a good idea to execute them when some aspect of the environment changes, for example when a new version of a database management system is introduced or a new version of a source code compiler is used.

                                   

Maintenance of a regression test suite should be carried out so it evolves over time in line with the software. As new functionality is added to a system new regression tests should be added and as old functionality is changed or removed so too should regression tests be changed or removed. As new tests are added a regression test suite may become very large. If all the tests have to be executed manually it may not be possible to execute them all every time the regression suite is used. In this case a subset of the test cases has to be chosen. This selection should be made in light of the latest changes that have been made to the software. Sometimes a regression test suite of automated tests can become so large that it is not always possible to execute them all. It may be possible and desirable to eliminate some test cases from a large regression test suite for example if they are repetitive (tests which exercise the same conditions) or can be combined (if they are always run together). Another approach is to eliminate test cases that have not found a defect for a long time (though this approach should be used with some care!).