Testing

After watching the JGR vid, I have a few questions. When testing a tire, how many laps does it take to have a feel for a tire, ok, if it's a bad tire, right away. However at that level we should be talking very subtle difference. Then if they have to test on race day, is the rider only allowed to test on the bike that's going to be raced? So in the interest of time could there be 2 or 3 bikes setup identical with different tires that a rider could jump off and onto a different bike? But then are they really that much the same? I had 2 jetskis 3 serial #s apart, visually identical, mechanically identical that rode totally different. At that level is it the same with the bikes? Or are manufacturing standards so good now that you can set bikes "identical"?
TM