You need to try to build an environment in training that is similar to a test which can be hard to do by yourself. My dogs energy at a test was always so much higher then training. I started to blow a duck call in the truck on the way to the grounds. I then would blow the call while setting up, shoot my starter pistol off a ton while setting up. Then I would run the test and try to get her to break under a controlled environment.
My dog wouldn't move a muscle during training but she was a big creeper at tests. I would set up all breaking stuff the days leading to a test. I tended to lean more on a heeling stick then I did the collar but I would use both. I was never worried about ruining her drive she always had enough!