If you haven’t changed a flat yet, now is the time to add learning and practicing it into your training schedule this week!  And yes there will be a test but it will be on the road when you least expect it.
If you missed the lesson or need a review, please go to this short video for a demo http://www.youtube.com/watch?v=i5K-DXt9djA .  Continue practicing until you feel confident that you can complete a change quickly at any time. 
Once you think you have mastered it -compare your fastest time with this guy!