Defect will rectified by the developer and change its status to Fixed but its tester duty to make sure that the application is a quality one so for the sake he will retest with the help of Steps to reproduce to check whether the defect is really fixed and on conformation tester will change the status to CLOSED as tester only has the right to close the defect.
Once the bug is fixed it is very important to ensure the other part of system haven't disturb or their might change to disturb other functionality therefore retesting is very very important after fixing bug then after bug can be CLOSED by tester
This is to ensure that the existing functionality is not damaged while fixing the problem/ defect.
This is quite important B'coz developer might not have the impact of other modules while fixing defect for one module. and we never know where & what is the impact of it so it is must to test the existing functionality of the application.
If is it a risk to test the while application then atleast test the main basic flows of each functionality End to End.
First: Reporting the bug (with appropriate Severity Priority and Reasons) After that the Defect have a proposed status. The development are fixed this defect and it become Resolved. QA team Retested this defect and on the end it become Closed.
After Bug fix the same or different kind of bug may or may not come. So it must be retested with the help of executing the same test cases with different Test Data.
To check whether the defect attains the state fixed and the rectified defect cause any impact on non defective part.this is the main reason to to do the defect retest.
It is important to retest a defect after it has been reported closed from the development. It is testers responcibility to regress the defect also tester has to test around the functionality for any new defects occured due to the closure of the defect.
