You have to set up a sparring partner and mate you trust who tries it out for you. Sometimes you need a close person on your team who is on your side for real and also wants to learn different stuff instead of the usual sparring riff that goes on these days.

You both talk it out and say theres a few things I want to work on, and you start slow move to half pace then amp the volume as you get used to exactly when and where some ideas will work and some dont, until you can you go at it full belt.

I mean its a rare situation someone is going to hold a glove up in your face and follow you around so you have to try and shoot around it.

Same thing for other rare situations: How can you practice power finishes on someone who's sharp and dancing around snappy trying to prove their point,its impossible? When you have ideas for when someone is tired at the end of a fight or doing desperate things, grappling or smothering or leaning,Pushing away with two gloves, over reaching jabs etc, you need someone to imitate those moves for you and its a trade off you both learn from and swap roles.
Same if youre going to fight a dude of a certain style you want your home boys to be able to imitate his moves, so that you can practice making them pay or disrupting their rhythm with your own.