Ember acceptance test andThen() doesn't wait until scroll events are complete

I need an emberJs acceptance test to be able to scroll to a certain point in the page and only then assert things about the page.

Both of these functions,

Ember.$('body').scrollTop(1000);

window.scroll(0,1000);

when followed by an

andThen(()=>{
    console.log('body', Ember.$('body').scrollTop());
}) 

print out that the body scrollTop position is at 108. I need it to be at 1000.

The only way I can get to the moment where body scrollTop is at 1000 is when I use this callback so far:

Ember.$('body').animate({scrollTop: 1000}, () => {
  console.log('body', Ember.$('body').scrollTop());
  staticWiz.assertHasGoToTopButton(true);
});

The problem here is that none of the test stuff exists by the point where this callback happens. I can't assert anything.

If I try to use assert.async() and done() with this callback, it makes it fire prematurely when the body scrollTop() is at 108:

const done = assert.async();
Ember.$('body').animate({scrollTop: 1000}, () => {
    console.log('body', Ember.$('body').scrollTop());
    staticWiz.assertHasGoToTopButton(true);
    done();
});

If I set a recurring timeout as a way to check the scroll position, it just stays at the same position of 108 forever.

const done = assert.async();
window.scroll(0, 1000);
const checkScroll = () => {
  console.log('body', Ember.$('body').scrollTop());
  if (Ember.$('body').scrollTop() === 1000) {
    staticWiz.assertHasGoToTopButton(true);
    done();
    return;
  }
  setTimeout(checkScroll, 1000);
};
checkScroll();

So. Any ideas? Has anyone gotten this working before for them, in an instance where you can't just have any degree of scrolling but need a specific number with an Emberjs acceptance test?