What key performance measure should a team maintain to measure the effectiveness of regression testing on a software patch?

Maintaining a measure of the rate of defect recurrence is crucial for assessing the effectiveness of regression testing following a software patch. This metric provides insight into whether the recent changes or fixes introduced by the patch have inadvertently reintroduced previous bugs or issues in the software. By tracking how often defects that were previously resolved reappear, the team can evaluate the stability of the application after modifications. High defect recurrence rates could indicate that the regression testing process is insufficient or that additional rigor is needed in testing practices, such as improving test coverage or refining test cases.

Other performance measures, like the number of test cases executed, percentage of successful test cases, or time taken to execute the tests, provide valuable information about the testing process itself but do not directly reflect the quality and reliability of the software post-patch. For instance, executing a high number of test cases or having a high success percentage can still occur in a context where defects are frequent, meaning that the ultimate goal of preventing defects from resurfacing is not being achieved. Thus, focusing on the recurrence of defects gives a clearer picture of regression testing effectiveness specifically in relation to the stability and functionality of the software after applying patches.