Capybara drag_to function throwing NotImplementedError

Capybara drag_to function throwing NotImplementedError

I have a Rails app that i'm trying to test the drag and drop functionality
on, I'm using capybara and rspec along with jquery ui for the dragging, it
works fine in the browser but I can't get a working test for it. The error
I get is as follows:
source_element.drag_to(dest_element)
NotImplementedError: NotImplementedError
I have a simple test file like so:
describe "display index page" do
it "try drag and drop" do
dest_element = find('#list_'+list.id.to_s+' #sortable')
source_element = find('#list_'+other_list.id.to_s)
source_element.drag_to dest_element
end
end
My Html looks like this (javascript is correctly configured and everything
works in the browser):
<ul id="sortable" class="ui-sortable">
<li id="list_20" class="sort">
<li id="list_121" class="sort">
<span>Content</span>
<ul id="sortable" class="ui-sortable"> </ul>
</li>
</ul>
Can anyone point out where I might be going wrong? I've tried looking
around for a good few hours but haven't been able to figure out what the
solution is.
Thanks in advance