A common way to implement A/B testing plugins is by creating alternative versions of the page you want to test as separate published pages. Whenever a visitor accesses a page that needs to be A/B-tested, the plugin simply redirects him or her from the original page URL to one of the URLs corresponding to the alternative pages.
Nelio A/B Testing does NOT do this. We don’t think this is a good idea. First, because the visitor may realize s/he has been redirected to a different URL (and thus, may become suspicious). Secondly, because there is the risk that search robots will index the alternative pages (and you don’t want that!). Finally, these published pages may pop up in other undesired locations (e.g. sitemap plug-ins, top X content plugins, …), since those plugins won’t distinguish between these alternative pages and the original ones.