Editing Software testing (section)

=== Regression testing ===
{{Main|Regression testing}}

Regression testing focuses on finding defects after a major code change has occurred. Specifically, it seeks to uncover [[software regression]]s, as degraded or lost features, including old bugs that have come back. Such regressions occur whenever software functionality that was previously working correctly, stops working as intended. Typically, regressions occur as an [[unintended consequence]] of program changes, when the newly developed part of the software collides with the previously existing code. Regression testing is typically the largest test effort in commercial software development,<ref>{{Cite book |last1=Ammann |first1=Paul |url=https://books.google.com/books?id=leokXF8pLY0C&pg=PA215 |title=Introduction to Software Testing |last2=Offutt |first2=Jeff |date=January 28, 2008 |publisher=[[Cambridge University Press]] |isbn=978-0-521-88038-1 |page=215 |access-date=November 29, 2017}}</ref> due to checking numerous details in prior software features, and even new software can be developed while using some old test cases to test parts of the new design to ensure prior functionality is still supported.

Common methods of regression testing include re-running previous sets of test cases and checking whether previously fixed faults have re-emerged. The depth of testing depends on the phase in the release process and the [[risk management|risk]] of the added features. They can either be complete, for changes added late in the release or deemed to be risky, or be very shallow, consisting of positive tests on each feature, if the changes are early in the release or deemed to be of low risk.