Recently in an interview i was asked this question. What is regression testing. I told them if a change is done in the application or if a bug is fixed by the developer, we use to do regression testing and ensure that this bug is not having impact on the other modules of the application.

Interviewer asked, so for example if I have 1000 test cases with me should we run and see all the test cases for this bug fixing?.

I was not able to answer this question. Please help me.

NOTE : [This question was asked by umashankar]

Regression testing is not done when a Bug is fixed. For the Fixed bug we only re-test the product to verify whether the bug has been resolved or not.

Regression testing actually refers to retesting of a previously tested program following modifications to ensure that faults have not been introduced or uncovered as a result of the changes made, and that the modified system still meets its requirements. It is performed whenever the software or its environment is changed.

Please note there is a difference between testing after a bug is fixed
(Commonly referred as Retesting of Defect) and when the complete software if modified or multiple changes have been made and the product is tested (Regression Testing)

Answer given by umasankar is right.
Actually interviewer was just want to know whether he has true exp. or showing the fake.

In real environment we only see whether the bug has been fixed, or can run some new test cases to catch new bug due to bug fixing.When product mobule is ready , at that time we should do regression, or you may see we should do regression on timely basis.

__________________
Brijesh Jain
brijesh.tester@yahoo.co.in
http://softwaretestingexpertise.blogspot.com

Regression testing is applying the previously failed and all the related tests on the modified built.

Eg. Let us suppose there are 25 test cases for the functionality. During the initial testing, the test case numbers 11 and 12 have failed and we can't continue testing unless the 2 bugs are resolved. In such case we first report the bugs. Once we receive the modified build from the developers, we apply previously failed test cases (i.e. 11 & 12) and all related test cases according to the bug (say 6, 7, 8 and 9). After that we continue applying the remaining test cases (i.e. 13 to 25).

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