This needs to be installed in your theme as a section

shopify-section-ab.liquid

{% javascript %}
function loadSection() { 
  var elArray = Array.prototype.slice.call(document.querySelectorAll(".shopify-section-ab"));
  if (window.parent.ThemeEditor !== undefined) {
    elArray.forEach(function(el) {
      el.classList.remove("ssab-neither");
      el.classList.add("ssab-editor");
    });
  } else {
    var cookie = "";
    if (getCookie("shopify_section_ab") === "") {
      if (Math.floor(Math.random() * 100) > 49) {
        cookie = "A";
        document.cookie = "shopify_section_ab=A";
      } else {
        cookie = "B";
        document.cookie = "shopify_section_ab=B";
      }
    } else {
      cookie = getCookie("shopify_section_ab");
    }
    if (cookie === "A") {
      elArray.forEach(function(el) {
        el.classList.remove("ssab-neither");
        el.classList.add("ssab-show-a");
      });
      ga("send", "event", "A/B Test", "A", "Test Campaign");
    } else {
      elArray.forEach(function(el) {
        el.classList.remove("ssab-neither");
        el.classList.add("ssab-show-b");
      });
      ga("send", "event", "A/B Test", "B", "Test Campaign");
    }
  }
}
document.addEventListener("shopify:section:load", function(event) {
  loadSection();
});
loadSection();

function getCookie(cname) {
  var name = cname + "=";
  var decodedCookie = decodeURIComponent(document.cookie);
  var ca = decodedCookie.split(";");
  for (var i = 0; i < ca.length; i++) {
    var c = ca[i];
    while (c.charAt(0) === " ") {
      c = c.substring(1);
    }
    if (c.indexOf(name) === 0) {
      return c.substring(name.length, c.length);
    }
  }
  return "";
}
{% endjavascript %}
{% schema %}
{
  "name": "A/B Test",
  "class": "shopify-section-ab index-section--flush ssab-neither",
  "settings": [],
  "presets": [
    {
      "name": "A/B Test",
      "category": "A/B Testing"
    }
  ]
}
{% endschema %}
{% stylesheet %}
.shopify-section-ab {
    display: none;
}
.shopify-section-ab.ssab-neither + *, .shopify-section-ab.ssab-show-b + * {
    display: none;
}
.shopify-section-ab.ssab-neither + * + *, .shopify-section-ab.ssab-show-a + * + * {
    display: none;
}
.shopify-section-ab.ssab-editor + *:before {
    content: "A/B Test - Version A ↓";
    display: block;
    text-align: center;
    color: #0c5460;
    background-color: #d1ecf1;
    border-color: #bee5eb;
    padding: 30px;
}
.shopify-section-ab.ssab-editor + *:after {
    content: "A/B Test - Version B ↓";
    display: block;
    text-align: center;
    color: #155724;
    background-color: #d4edda;
    border-color: #c3e6cb;
    padding: 30px;
}
.shopify-section-ab.ssab-editor + * + *:after {
    content: "A/B Test - End";
    display: block;
    text-align: center;
    color: #856404;
    background-color: #fff3cd;
    border-color: #ffeeba;
    padding: 30px;
}
{% endstylesheet %}