There is zero reason to test a system like that over the actual target.
The first use wouldn’t be a test.
Why is a secret balloon white, against a blue sky?
The test is to see how we react.
It could be checking out to prevailing winds Perhaps China is worried about nuclear fallout when they nukas us Or They could have hundreds of thousands of balloons ready to go, just float over this country and then whatever they’re gonna do with them they are going to do. Maybe they just need to know to prevailing wind across the country to do that.