It is testable, and not all science involves direct observation. It can be falsified. Say, if you find a human fossil in rock that is undoubtedly from 80 million years ago. The scientists would have no choice but to change the theory, or abandon it altogether. This is the nature of science. I'm sure there are scientists out there wishing they could find this, because they would be one of the the most famous scientists of the last 100 years.
Take Creation Science, however. It's non-testable unless God starts creating stuff again. It doesn't have to adapt to new evidence because new evidence must adapt to it. In opposition to scientific method, it cannot be falsified because the first tenet is that it is true (while evolution is that this is the best we know based on what knowledge we have, subject to change). And it can't predict beyond what's already written.
Seriously, evolution has been around a long time, and while small parts have been challenged and changed over the years, the basic concept hasn't been successfully challenged yet in the open peer-review scientific community.
But evolutionists have been back pedaling since the start of the theory, it's too flexible to be meaningful or decisive. When a theory can cover any combination of facts or a total lack of facts, it doesn't contribute to knowledge. Its like a tautology: something that is true but in a trival way.
What's even worse is when turn of the century philosophers like Nietzche, Marx and Darwin point to evolution as a way of getting rid of God (and specifically Christianity), then they are taking a trivial physical theory and making serve a theological aim.
The problem is this: can any act of creation (the making of an airplane). Limited by the principles of physicalistic science, prove that it was not created by a mind. That is what evolution, in its fullest form, is really trying to do. Its a philosophically nonsensical task.