That doesn't follow, though. The obvious example would be that if Jesus actually rose from the dead by a miracle, then people who were present could see him and put their hands on his scars.
Is the supernatural inherently not scientifically testable?
Absolutely.
It does not follow that it could never be observed at all, if it exists.
I'm saying that we have yet to have observe something which can be proven to be supernatural.
Asking whether evidence exists that a phenomenon is strictly natural presumes there exists evidence of something other than nature to classify against. As yet, such evidence to the contrary doesn't exist, so for the time being, all evidence of any phenomenon is of its natural state by definition.
>It does not follow that it could never be observed at all, if it exists.
The unfortunate paradox of needing to provide evidence of the supernatural is that any such evidence would, by definition, need to be natural, and would contradict the premise. So if it can be observed to begin with, that's evidence that it isn't supernatural.