Defect tracking happens thru multiple edits on the issue. The issue record is updated by the one who found the issue, by the managers and by the people who fix the issue.
Tested by will be the username of the tester who added the bug.
Expected Closure Date - Choose the date of closure.
Closed in Version - select the version if the bug is closed.
Comments - Enter any comments for the bug.
Root Cause - this is usually done by the developer or leads.
Resolution - This is to be entered by the person who fixed the bug.
Comments History - This will be a display field that will show all the comments entered about the bug.