Pro-rata charges not working in test mode

I’m trying to test subscription package changes but it seems that whatever I do, I’m not seeing any pro-rating of charges. The docs seem to say this should happen but I don’t know if there is a problem on my end or if it’s a limitation of test mode.

I’m really hoping it’s not the latter because that would make it impossible to check that we are handling all subscription changes correctly.

Any help/advice would be very appreciated,

Thanks