CustomEvent('mousedown', {
      bubbles: true,
      cancelable: true,
      composed: true
    });
    ev.clientX = ev.clientY = 0;
    el.dispatchEvent(ev);
    assert.equal(el.stream.length, 1);
    for (var i = 0; i < 10; i++) {
      ev = new CustomEvent(
        i === 9 ? 'mouseup' : 'mousemove',
        {bubbles: true, cancelable: true, composed: true}
      );
      ev.clientX = ev.clientY = 10 * i;
      el.dispatchEvent(ev);
    }
    assert.equal(el.stream.length, 2, 'expected only down and up')