Our scrum team consisted of 2 developers and 2 testers and had the velocity of 21 with 2 week sprint.
In one particular sprint, a tester had a planned vacation (not for the entire sprint but some part of the sprint). The team started work with upto 12 story points. As each story was completed, the tester started testing it. The development was way ahead of the tester as expected. However, the working tester fell sick and was not able to complete testing and the stories were not considered done (per our definition).