Before you consider yourself "done" testing, go back and double check

Many teams track release status by tracking the status of tickets in the release. A ticket might be a story, feature, or some other unit used to tie work to a release number. That is, if a release has 10 tickets in it (regardless of if those tickets are bugs, features, or other), the release isn't done until those 10 tickets are done. For most teams, testing is part of the ticket workflow.

When you're working in this type of environment, you often do your test planning for the release upfront. You might charter testing for certain tickets together or break up testing across multiple testers by assigning testers specific tickets. When you do this, you always run the risk of someone adding another ticket into the mix before you've finished your testing. While most teams (hopefully) have some communication methods for this type of change, sometimes tickets sneak in.

Whenever I'm testing a release like this, the last thing I do before I call my testing "done" is to go back and make sure no new tickets were added. Most tools make this very easy to do. All I'm trying to do is reconcile my testing efforts with the release before I hand it off to the next stage. Occasionally, I catch something that got slipped in that my testing missed.