I would say that if the test is for something serious, do it now. Your baby needs a healthy mama first and foremost.
If it's not that important, then I think it probably would be good to delay it a bit. Waiting until your baby is taking solids is a great idea. At 7 months, my baby is still exclusively breastfed, but I would have introduced solids at about 6 months for something like that.
I'd see if your baby will take a bottle or sippy cup now. We waited until DS was about 4 months old before giving him a bottle, and he acted like he'd been drinking from one his whole life. He's only had less than 10 bottles, but he has always been fine with taking one whenever we needed to give him one.
You shouldn't have a hard time getting enough expressed milk ahead of time since you know it's coming. I would probably try to pump one side while the baby nurses on the other side each morning for about a month or so before the test. It's always easiest to pump in the morning, and having the baby nursing on the other side makes it that much easier.
If the baby takes well to the bottle or cup, then you really don't need to worry about solids too much. Just make sure that she's willing to take a bottle at the most "snuggly" nursing sessions, like just before going to sleep at night.