Darwin’s theory meets that criteria.
Proponents of intelligent design have yet to develop a testable hypothesis that could get it into the scientific arena.
The only argument I’ve ever heard from intelligent designers has to do with their incredulity about mechanisms behind evolution. Their stance is that the irreducible complexity of life must have had a designer. I’ve spoken with proponents of intelligent design, and I’ve read their writings. The only thing they have to say is that they accept the reality of microevolution, as they must if they believe in things like flu shots, but they do not see how one species might develop from another.
I feel a certain sympathy with that view. There is clearly intelligence at work in nature that is well beyond human comprehension. I’m not uncomfortable with the naming of that intelligence as God, but I would hesitate to be so specific as to say that it is God as described in the Bible. That is the rather huge leap of faith that proponents of intelligent design are asking that we make in science classes. It is not science.