Untestable? Perhaps. Perhaps not. Just because something isn't testable, doesn't mean it's not observable.
On need look no further than the HIV virus. Science has been observing it's evolutionary progress for well over 25 years now. The same can be said for hundreds of thousands of other virus and bacterium that have been under relentless study since the time of Pasteur, Cohn and Koch.
“Untestable? Perhaps. Perhaps not. Just because something isn't testable, doesn't mean it's not observable.” [excerpt]Yeah, fine.