There are a variety of ways to test canine intelligence. There are tests that measure a dog’s temperament; tests that rate a dog’s problem solving skills and; tests that rank a dog’s cognitive abilities (e.g. distinguishing between diffferent categories of photographs).
Keep in mind that what may pass for intelligent behavior for one breed of dog may not be an accurate measure of intelligence for another breed. For example, a Basset Hound may have superior scent skills but perform poorly at herding a gaggle of geese, while a Belgian Sheepdog can herd the geese with no problem but not be alerted to the scent of a rabbit who recently passed his way.