There is no one simple answer to this question. This has been a painful issue throughout many projects.
Managing duplicate defects depends on the efficient coordination established within the team. Regular team meetings/calls during test execution phase identify any such instances and can be avoided even before other teams notice this. Secondary approach is to ensure that the delegation of test execution is done in such a way that no people in the team work on testing same or similar functionality.
See.... we cannot test same test cases in 3 testers. right.
Suppose tester did same test cases and produced 3 defects. In this case we can reject 2 defects as a duplicate and mentioned External TIL refference number field.
In normal scenario the defects are assigned to the test lead / development lead....He will be taking care of the duplicates... he goes through each and every defect before assining the same to any of the developer/programmer... he will have a good knowledge of the defects and if he finds that the defect has already occured he will mark it as duplicate and will send it back to the tester with refering to the existing defect number....
Assiging the same test cases to 3 testers is possible in my project i feel it's totally 3 depends on project mine is product which cotains diff clients but same files... so there is a chance to raise the duplicate issues...
Coming to deletion if it's excel sheet then tester/lead can remove the issues or else if it;s a defect tracker test lead can close or delete the issues we can intimate the same to client if reported to him.
in one of my project we had 5 modules and 5 tester the defect was realted to date functionality that was identified in 5 modules and raised by 5 tester's under their modules but the function for the date functionality was one and developed by a single developer so developer has accepted the first defect and changed status of remaining defects to Duplicate and closed forcefully.
