To answer this question, we need to understand the concepts of re-testing and regression testing.
Re-testing refers to running a test again to ensure that a specific issue or bug has been fixed. It involves re-executing the same test case that previously failed to verify if the fix has resolved the problem.
Regression testing, on the other hand, is the process of testing the unchanged parts of a software system to ensure that the modifications or bug fixes have not introduced any new defects or caused unexpected side effects. It aims to validate that the existing functionality has not been affected by the changes.
Now let's go through each option to understand why it is correct or incorrect:
Option A) re-testing is running a test again; regression testing looks for unexpected side effects - This option is correct. It accurately describes the difference between re-testing and regression testing. Re-testing involves running a test again, while regression testing focuses on identifying unexpected side effects caused by changes.
Option B) re-testing looks for unexpected side effects; regression testing is repeating those tests - This option is incorrect. It incorrectly states that re-testing looks for unexpected side effects, which is the role of regression testing.
Option C) re-testing is done after faults are fixed; regression testing is done earlier - This option is incorrect. It incorrectly suggests that re-testing is performed after faults are fixed, while in reality, it is done to verify the effectiveness of the fix. Regression testing, on the other hand, can be performed at any stage of the development cycle to ensure that changes do not introduce new issues.
Option D) re-testing uses different environments, regression testing uses the same environment - This option is incorrect. The environment used for testing does not define the difference between re-testing and regression testing. Both types of testing can be performed in the same or different environments based on the specific requirements.
Option E) re-testing is done by developers, regression testing is done by independent testers - This option is incorrect. The responsibility for re-testing and regression testing can vary depending on the organization and the testing team. While developers may perform re-testing, independent testers can also be involved in both re-testing and regression testing.
Therefore, the correct answer is A) re-testing is running a test again; regression testing looks for unexpected side effects.