<% content_for :title, "A/B testing - GOV.UK" %>
<% content_for :extra_headers do %>
  <%= @requested_variant.analytics_meta_tag.html_safe %>
  <meta name="robots" content="noindex">
<% end %>

<main id="content" role="main" class="govuk-grid-column-two-thirds">
  <%= render "govuk_publishing_components/components/title", {
    title: "This is a test page"
  } %>

  <p class="govuk-body"><%= t('ab_testing.explanation') %></p>

  <p class="govuk-body"><%= t('ab_testing.two_versions') %> <strong class="ab-example-group"><%= @requested_variant.variant?("A") ? t('a') : t('b') %></strong> <%= t('ab_testing.version') %>.</p>

  <p class="govuk-body"><%= t('ab_testing.visit_govuk_html') %></p>
</main>

<% content_for :title, "A/B testing - GOV.UK" %>
<% content_for :extra_headers do %>
  <%= @requested_variant.analytics_meta_tag.html_safe %>
  <meta name="robots" content="noindex">
<% end %>

<main id="content" role="main" class="govuk-main-wrapper">
  <div class="govuk-grid-row">
    <div class="govuk-grid-column-two-thirds">
      <%= render "govuk_publishing_components/components/title", {
        title: "This is a test page"
      } %>

      <p class="govuk-body"><%= t('ab_testing.explanation') %></p>

      <p class="govuk-body"><%= t('ab_testing.two_versions') %> <strong class="ab-example-group"><%= @requested_variant.variant?("A") ? t('a') : t('b') %></strong> <%= t('ab_testing.version') %>.</p>

      <p class="govuk-body"><%= t('ab_testing.visit_govuk_html') %></p>
    </div>
  </div>
</main>

Fix A/B testing page layout
Fix A/B testing page layout

The page was missing the grid row element
