Regression testing

Regression testing is a type of software testing that verifies that software previously developed and tested still performs correctly even after it was changed or interfaced with other software. Changes may include software enhancements, patches, configuration changes, etc. During regression testing, new software bugs or regressions may be uncovered. Sometimes a software change impact analysis is performed to determine what areas could be affected by the proposed changes. These areas may include functional and non-functional areas of the system.

The purpose of regression testing is to ensure that changes such as those mentioned above have not introduced new faults.[1] One of the main reasons for regression testing is to determine whether a change in one part of the software affects other parts of the software.[2]

Common methods of regression testing include re-running previously completed tests and checking whether program behavior has changed and whether previously fixed faults have re-emerged. Regression testing can be performed to test a system efficiently by systematically selecting the appropriate minimum set of tests needed to adequately cover a particular change.

Contrast with non-regression testing (usually validation-test for a new issue), which aims to verify whether, after introducing or updating a given software application, the change has had the intended effect.

Background

As software is fixed or changed, emergence of new faults and/or re-emergence of old faults is quite common. Sometimes re-emergence occurs because a fix gets lost through poor revision control practices (or simple human error in revision control). 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. Frequently, a fix for a problem in one area inadvertently causes a software bug in another area. Finally, it may happen that, when some feature is redesigned, some of the same mistakes that were made in the original implementation of the feature are made in the redesign.

Therefore, in most software development situations, it is considered good coding practice, when a bug is located and fixed, to record a test that exposes the bug and re-run that test regularly after subsequent changes to the program.[3] Although this may be done through manual testing procedures using programming techniques, it is often done using automated testing tools.[4] Such a test suite contains software tools that allow the testing environment to execute all the regression test cases automatically; some projects even set up automated systems to re-run all regression tests at specified intervals and report any failures (which could imply a regression or an out-of-date test).[5] Common strategies are to run such a system after every successful compile (for small projects), every night, or once a week. Those strategies can be automated by an external tool.

Regression testing is an integral part of the extreme programming software development method. In this method, design documents are replaced by extensive, repeatable, and automated testing of the entire software package throughout each stage of the software development process. Regression testing is done after functional testing has concluded, to verify that the other functionalities are working.

In the corporate world, regression testing has traditionally been performed by a software quality assurance team after the development team has completed work. However, defects found at this stage are the most costly to fix. This problem is being addressed by the rise of unit testing. Although developers have always written test cases as part of the development cycle, these test cases have generally been either functional tests or unit tests that verify only intended outcomes. Developer testing compels a developer to focus on unit testing and to include both positive and negative test cases.[6]

Techniques

The various regression testing techniques are:

Retest all

This technique checks all the test cases on the current program to check its integrity. Though it is expensive as it needs to re-run all the cases, it ensures that there are no errors because of the modified code.[7]

Regression test selection

Unlike Retest all, This technique runs a part of the test suite (owing to the cost of retest all) if cost of selecting the part of test suite is less than retest all technique.[7]

Test case prioritization

Prioritize the test cases so as to increase a test suite's rate of fault detection. Test case prioritization techniques schedule test cases so that the test cases that are higher in priority are executed before the test cases that have a lesser priority.[7]

Types of test case prioritization

Hybrid

This technique is a Hybrid Approach of both Regression Test Selection and Test Case Prioritization. Algorithms for the approach that have been proposed are test selection algorithm and hybrid technique proposed[7]

Benefits and drawbacks

Regression testing is performed when changes are made to the existing functionality of the software or if there is a bug fix in the software. Regression testing can be achieved through multiple approaches, if a test all approach is followed it provides certainty that the changes made to the software have not affected the existing functionalities, which are unaltered, in any way.[8]

In an agile project management process, where the software development life cycles are very short, resources are scarce and changes to the software are very frequent; Regression testing might introduce a lot of unnecessary overheads.[8]

Typically, regression testing is carried out by automation tools, but the existing generation of regression testing tools is not equipped to handle database application. For this reason, performing a regression test on a database application could prove to be taxing as it would require a great deal of manual effort.[9]

Moreover, performing regression testing in a software development environment which tends to use black box components from a third party can get a bit tricky as any change in the third party component may interfere with the rest of the system and performing regression testing on a third party component is difficult because it is an unknown entity.[8]

Uses

Regression testing can be used not only for testing the correctness of a program, but often also for tracking the quality of its output.[10] For instance, in the design of a compiler, regression testing could track the code size, and the time it takes to compile and execute the test suite cases.

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

Regression tests can be broadly categorized as functional tests or unit tests. Functional tests exercise the complete program with various inputs. Unit tests exercise individual functions, subroutines, or object methods. Both functional testing tools and unit testing tools tend to be automated and a third-party product that are not part of the compiler suite. A functional test may be a scripted series of program inputs, possibly even involving an automated mechanism for controlling mouse movements and clicks. A unit test may be a set of separate functions within the code itself, or a driver layer that links to the code without altering the code being tested.

See also

References

  1. ↑ Myers, Glenford (2004). The Art of Software Testing. Wiley. ISBN 978-0-471-46912-4.
  2. ↑ Savenkov, Roman (2008). How to Become a Software Tester. Roman Savenkov Consulting. p. 386. ISBN 978-0-615-23372-7.
  3. ↑ Kolawa, Adam; Huizinga, Dorota (2007). Automated Defect Prevention: Best Practices in Software Management. Wiley-IEEE Computer Society Press. p. 73. ISBN 0-470-04212-5.
  4. ↑ Automate Regression Tests When Feasible, Automated Testing: Selected Best Practices, Elfriede Dustin, Safari Books Online
  5. ↑ daVeiga, Nada (February 2008). "Change Code Without Fear: Utilize a Regression Safety Net". Dr. Dobb's Journal.
  6. ↑ Dudney, Bill (2004-12-08). "Developer Testing Is 'In': An interview with Alberto Savoia and Kent Beck". Retrieved 2007-11-29.
  7. 1 2 3 4 "UNDERSTANDING REGRESSION TESTING TECHNIQUES". Citeseerx. 2008.
  8. 1 2 3 "Regression Testing Minimisation, Selection and Prioritisation: A Survey; S. Yoo, M. Harman". Published online in Wiley InterScience. 2007.
  9. ↑ "Efficient Regression Tests for Database Applications". Springer Journal. 2006.
  10. ↑ Kolawa, Adam. "Regression Testing, Programmer to Programmer". Wrox.

External links

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