Check slider content using backstopjs

Question

I have used bxslider and want to check the 2nd and 3rd child of the slider using backstopjs. I checked using the delay event in both the backstop.json and the bxslider script. it generates references for the child content of the slider. but fails to generate appropriate references of the items.

1) This is my html

<ul class="bxslider">
      <li><img src="http://grab.by/NplU" title="Funky roots" /></li>
      <li><img src="http://grab.by/Npm2" title="The long and winding road" /></li>
      <li><img src="http://grab.by/Npma" title="Happy trees" /></li>
    </ul>

2) bxslider initialize script

$('.bxslider').bxSlider({
        auto: true,
        autoDelay: 900
    });

3) this is my backstopjs script

{
  "viewports": [
    {
      "name": "desktop",
      "width": 1600,
      "height": 900
    }
  ],
  "scenarios": [
    {
      "label": "Bxslider",
      "url": "http://localhost/jquery-bxslider/",
      "hideSelectors": [],
      "removeSelectors": [],
      "selectors": [
        "section ul li:nth-of-type(1)",
        "section ul li:nth-of-type(2)",
        "section ul li:nth-of-type(3)"
      ],
      "readyEvent": null,
      "delay": 1000,
      "misMatchThreshold" : 0.1,
      "onReadyScript": "onReady.js"
    }
  ]
}