thats up to you. It depends on where you live, honestly. If it's still pretty cold where you live, theres probably been little mosquito activity and you can just start up the treatment again. If you live in alabama like me, you might want to consider getting the tests done to be ont he safe side, some heartworm treatments can be deadly for dogs that already have heartworms.
i am not very familiar with revolution being used as heartworm prevetative as we don't use it for that in our clinic. it would be a waste to get the dog tested if you only missed a month as heartworms take six months to show up in a blood test. when we have clients that miss a month of heartguard or interceptor we tell them to continue giving the prevention on their regular schedule and retest the dog in 6 months. you may want to check with your vet to see if the same rule applies to revolution.