warranty in the first place. It's a manufacturer's warranty (not a dealer's warranty). If you took the car in for specific repairs and the dealer sees that you may have done something to void the express warranty, the dealer would alert the manufacturer when they submit the claim to see if it will be covered by the manufacturer (before the dealer does the work) and based on what the dealer submits in its request for coverage the manufacturer decides whether it will pay.
Second question: Does the manufacturer's warranty state in writing that a dyno session voids the warranty. If it's not in writing...some dealer service rep saying it's voided...means squat.