govuk_elements_form_builder_capybara_patch.rb

module Capybara
  module Node
    module Actions

      alias_method :old_check, :check
      alias_method :old_uncheck, :uncheck

      def check(locator, options = {})
        Capybara.current_session.evaluate_script js_element_check(locator, true)
      end

      def uncheck(locator, options = {})
        Capybara.current_session.evaluate_script js_element_check(locator, false)
      end

      private

      def js_find_by_id locator
        element = <<-SCRIPT.strip.gsub(/\s+/,' ')
          element = (function () {
            var element = document.getElementById(\"#{locator}\");
            return element;
           })()
        SCRIPT
      end

      def js_element_check locator, switch = true
        checkbox = js_find_by_id(locator)
        <<-SCRIPT
          (function () {
            #{checkbox}.checked = #{switch}
           })()
        SCRIPT
      end

    end
  end
end

The Gov uk element for builder uses pseudo elements and javascript to style the checkboxes. as a result the input checkbox fields cannot be checked with the standard check/uncheck helpers (using capybara 2.5.0 with poltergeist 1.14.0 at least).

This patches the aforementioned helpers to use javascript on the resulting dom.