About a year ago I fostered a kitten from the Victoria SPCA who was "wobbly". After a series of trips to the vet everything but FIP was ruled out. This meant a death sentence for my little Bitsy. Because of this incident with my foster kitty I learned a great deal about FIP in an attempt to help her. One thing I do know is that there is no test. One can only test for the presence of Corona virus antibodies. This does not mean the cat has FIP. In fact many cats come in contact with the Corona virus and only rarely does it mutate to the FIP form.
Dr. Addy in Scotland is the foremost expert in FIP and has done a great deal of research. Much information can be gleaned from her website.