Identifying Cat Urine Stains on Hardwood Floor?

We recently saw some black staining and possible rotten wood in a small corner area of our newly refinished wood floor. At first we thought it could be a leaking water pipe in the wall, but now we're wondering if it wasn't from cat urine. Our 11 yr. old cat who has never urinated anywhere except the litter box has recently wet on the small bathroom rugs a few times. The vet diagnosed a UTI and we've been giving the cat meds.

In the area of the black stains and dry, rough section on the wood floor, we have never seen any liquid and there is absolutely no cat urine smell. Even if the cat only urinated there once or twice, wouldn't it smell (since that smell is so strong and foul)? The only way to know if we have a leaking pipe will be to tear out a hole in the wall which will end up being an extensive repair. But if we can determine it was cat urine, then we would simply have the floor repaired. Does anyone know how we can determine if it is or is not a stain from cat urine?