We adopted what we thought was a feral cat. A small wet kitten with wounds all over its face showed up one day. We took it to the vet telling them we would care for it. They said they would check it for FIV - same as AIDS in humans. If positive they would put it down. They clip the tip of the left ear which is the universal sign of a neutered feral cat.
This kitten bonded with our pet cat and both are buds now.
I adopted to kittens that wondered up to where I worked one day. After a few days I brought them home. They owned us for 46 years. There came a time when we had to put them down and I cried like a baby. The only cats I’ve ever owned.