spec/fixtures/sitemap/sitemap_index.xml

<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
   <sitemap>
     <loc>http://www.example.com/sitemap1.xml</loc>
     <lastmod>2004-10-01T18:23:17+00:00</lastmod>
   </sitemap>
   <sitemap>
     <loc>http://www.example.com/sitemap2.xml</loc>
     <lastmod>2005-01-01</lastmod>
   </sitemap>
</sitemapindex>