engsohere - if you have friends who have pets, ask them who their vet is, and if they like the vet. Word of mouth is a good way to go.

Or ask your local Humane Society who they use, and how to go about finding a good vet.

Here are some tips from one site...
How to Find a Veterinarian
From your Veterinary Medicine Guide

Whether you are new to an area, just got a pet, or looking for a second opinion, here are some tips on finding a veterinarian.

Difficulty Level: Easy Time Required: varies

Here's How:

1. When searching for a new vet (relocation, new pet) ask friends, family, and co-workers who they see and why they like that vet.
2. When seeking a second opinion or referral, first ask your current vet if possible.
3. If you feel uncomfortable about asking your present vet for a referral, start with step one above.
4. Call the state veterinary medical association (VMA) for specialist referrals in your location.
5. The AVMA (http://www.avma.org) also has state veterinary medical association contact information online.
6. There are several sites online that will do a localized veterinarian or veterinary hospital search for you (see 'Related Links' below).
7. The Yellow Pages are also an option for initial research when finding a veterinarian.
8. Once you have the names of some veterinarians in your area who see the species of pets or animals that you have, the next step is to call or stop by the office.
9. Is the reception staff friendly, helpful, and knowledgeable?
10. Will the office hours work with your schedule and lifestyle?
11. What about emergency coverage after hours and on holidays?
12. Is the veterinary staff (doctors, technicians, assistants) professional and knowledgeable?
13. Do the staff members have a good 'bedside manner' when relating to you and your pet?
14. If the vet and/or hospital that you have selected do not meet these criteria, you may want to keep looking until you can be assured that your pet is receiving the best possible care.
This Google search link has a few options to click on: http://www.google.ca/search?hl=en&q=...e+Search&meta=

If he was a stray - bless you for taking him in. He should have had a medical checkup right away, but now would be a good time.

As for tests, I don't know anyone here who could answer that. The vet will examine your cat. It could be as simple as kitty's having worms (inside or outside kitty?), or a symptom of something else. Even a change in food can help, and might solve the problem.

Please ask your friends, and get your furbuddy to a vet soon.