function testCubicBezierDrag(opts) {
                    makeTimingFuncUI("cubic-bezier(.42, 0, .58 ,1)");
                    var $downItem = $(timingFuncEditor[opts.downItem]),
                        $dragItem = $(timingFuncEditor[opts.dragItem]);

                    eventAtOffset("mousedown", $downItem, opts.clickAt);
                    eventAtOffset("mousemove", $dragItem, opts.dragTo);
                    $downItem.trigger("mouseup");
                    expectArraysToBeEqual(timingFuncEditor._cubicBezierCoords, opts.expected);
                }
Test a drag event on the given UI element.
@param {object} opts The parameters to test:
    downItem: The (string) name of the member of BezierCurveEditor
         that references the element to mousedown on to drag.
    clickAt: An [x, y] array specifying the simulated x/y mouse position as an offset of the
         item's width/height.
    dragItem: The (string) name of the member of BezierCurveEditor
         that references the element to drag item to.
    dragTo: An [x, y] array specifying the location to drag to, using the same convention as clickAt.
    expected: The expected array of values for _cubicBezierCoords.