# File lib/action_dispatch/testing/assertions/selector.rb, line 413
      def assert_select_email(&block)
        deliveries = ActionMailer::Base.deliveries
        assert !deliveries.empty?, "No e-mail in delivery list"

        for delivery in deliveries
          for part in (delivery.parts.empty? ? [delivery] : delivery.parts)
            if part["Content-Type"].to_s =~ /^text\/html\W/
              root = HTML::Document.new(part.body.to_s).root
              assert_select root, ":root", &block
            end
          end
        end
      end