Wait, I'm pretty sure that if these measurements had shown a collapse, that would have to be taken as disproving many worlds. You can't very well have many worlds when your wavefunction is physically collapsing all the time before those worlds can diverge. So it is actually kind of testable, since a test was just performed that could have ruled it out. Maybe you're saying that it's untestable relative to unmeasurable collapses of the wavefunction. But if those collapses are contrived to be unmeasurable, doesn't that make them kind of, well, pointless?