Confirmation testing or re-testing: When a test fails because of the defect then that defect is reported and a new version of the software is expected that has had the defect fixed. In this case we need to execute the test again to confirm that whether the defect got actually fixed or not.
This is known as confirmation testing and also known as re-testing. It is important to ensure that the test is executed in exactly the same way it was the first time using the same inputs, data and environments.
Hence, when the change is made to the defect in order to fix it then confirmation testing or re-testing is helpful.