Yes, it's testable, but you can't test from single cell to a human being, which is what the theory puts foward. As such the whole theory is untestable and therefore unprovable. However, we can test much smaller timescales ans this in addition to understanding of selective breeding, the fosil record and an increasing understanding of genetics indicates the theory is correct.

However, not of that constitutes difinitive proof. It's like saying Newton's Laws of Motion are concrete and provable, until Einstien comes along and proves that in 0.1% of cases they don't work.

They're still as close as you or I will ever need but thay're also technically wrong.

Evolution might also be almost right but actually wrong.

So what the Pope is saying is perfectly logical. His intent in saying it might be something else.