Possible Clues:

• Cavalier's challenge?
• Challenge for car mounted reportedly by river
• Try out various treats, do!
• Driver's license prerequisite
• Try out new taste, or start to drool
• As check of transport, moved boat, say, to river
• Sort date out for critical examination of product
• Examination of vehicle's performance on highway
• Stated or otherwise, a jalopy needs it
• Heaps fail it!