I propose a different approach: preventively treat the cat against intestinal worms and only go to the vet if s/he shows any signs of illness.
If the cat ate those animals, intestinal worms are the most common parasites s/he might get that way. There are numerous products available to treat worms, like pills or pastes to be ingested or a liquid that is applied to the back of the neck. The latter one is my personal recommendation, because most cats are finnicky and refuse to swallow medicine.
It's important that you don't treat a cat with anti-parasites for a dog. There are certain products for dogs that act like a neuro toxin in cats and kill them. Be safe and buy a product formulated for cats.
The advantage of this approach is that you can treat the parasites before they can cause any damage or health problems. If your cat didn't catch any parasites after all, you save him/her a trip to the vet (and you save the money for the test).
Additional things you should keep an eye on:
- If your cat starts scratching a lot, s/he might have fleas.
- If s/he gets unusual hairloss, consult a vet. The seasonal change of coat is not unusual, but if your cat gets bald patches, better see a vet. It could be caused by fungi or parasites from the killed animals.
- Any strong change in behavior, like sudden hiding away, listlessness or lack of appetite warrants a visit to the vet.
- Vomiting and/or diarhea can have so many different causes that it's best to have a vet find the cause and the right treatment.