test/dummy/app/views/layouts/application.html.erb

<!DOCTYPE html>
<html>
  <head>
    <title>Dummy</title>
    <%= csrf_meta_tags %>
  </head>

  <body>
    <% if current_user %>
      <%= link_to "Sign out", users_sign_out_path %>
    <% else %>
      <%= link_to "Sign in", users_sign_in_path %>
    <% end %>

    <%= debug current_user.inspect %>

    <% flash.each do |kind, msg| %>
      <%= tag.div(class: kind) { msg } %>
    <% end %>

    <%= yield %>
  </body>
</html>