Currently WheelEventTestMonitor doesn't know about momentum animations, but even if it did, it's impossible to write a test that determines whether an "End" momentum event has interrupted the momentum. This is because we start the animator when we see the momentum "Began", ignoring the rest of the momentum changed. The animator runs on a display link callback on the scrolling thread, so we don't have a reliable way to know when the animator has run enough frames to move content around.
<rdar://problem/85716526>