I’ve said it before but I’ll say it again - the most specific form of training for tennis is playing tennis! Thus, tennis training - which includes on-court drills, live ball hitting, practice sets (and even tournament matches) - is the truest form of ‘sport-specific physical training’ for tennis.
So if you hear someone talk about ‘sport-specific training’ and they’re jumping on a bosu ball, performing shadow swings on the beach or some other random exercise, that is NOT sport specificity.