Because it seems to me to be rather redundant to propose a testable hypothesis to demonstrate intelligent design is present and operative in the universe when the hypothesis is an instrument of intelligent design in and of itself.
But maybe the request is for a testable hypothesis to demonstrate how intelligent design comes about, or what is the extent of its manifestation in the known universe, or whether intelligent design can exist without a mechanism to drive it, or whether intelligent design is a necessary attribute of both the subject and object of science before science can even begin its work.
Take your pick from any of the above, and I will try to create a hypothesis to suit it. At the same time, I would ask that those who support the Theory of Evolution design a testable hypothesis to demonstrate the mechanism whereby a living species can emerge without the agents of either intelligence or design.
That statement only makes sense if you'd be trying to prove that humans designed and created the universe.