We usually miss out.

My admin often helps me mitigate the problem by letting me have the band during Activity period or similar.
They also communicate well about when and who is testing so I can plan around it.
I have 8th grade in our HS band and they often work to put both JH and HS on the same day.

We did have one year that they put the entire HS band in the gym first period, sitting doing absolutely nothing so they could put 5 JH kids in the band room for testing. That was frustrating and straight up wrong but I couldn't convince them otherwise. That admin only lasted one year anyway though.