I was really happy with the scrum process at SOE during the development of DC. One of the requirements we had was that there had to be an "in testing" column on our scrum boards. Any task that had a testable piece would then be moved into the testing column and sent to QA. A QA rep was then the only person who could move that scrum card out of testing and put it in finished. If the found a bug, it was addressed and fixed with the initial task. During early development, this worked decently to catch a number of bugs before engineers moved on to a new sprint.