I don't have a resource but wanted to mention mfg companies guaranteeing their products.
Ivermectin for instance will guarantee their product (pay for treatment if dog gets HW) only if you purchase it from your vet. Not on line.
They will also guarantee under your vets protocol of HW occult. If your vet recommends testing every year you must to this to be covered. If every 2 years is your vet's protocol than you are covered testing every 2 years.