Test that all components render without error

* Require webmock minitest for `stub_request` in
stub_shared_component_locales
* Add an ActiveSupport concern to avoid hitting Slimmer for component
guide requests (this matches the way we avoid hitting Slimmer when
using Jasmine)
* This doesn’t explicitly run Javascript, accessibility tests will not
yet be running

test/integration/component_guide_test.rb

@@ -0,0 +1,38 @@
+require 'integration_test_helper'
+require 'webmock/minitest'
+require 'slimmer/test_helpers/govuk_components'
+
+module GovukPublishingComponentsSkipSlimmer
+  extend ActiveSupport::Concern
+
+  included do
+    before_action :skip_slimmer
+  end
+
+  def skip_slimmer
+    response.headers[Slimmer::Headers::SKIP_HEADER] = "true" unless ENV['USE_SLIMMER'] == "true"
+  end
+end
+
+GovukPublishingComponents::ApplicationController.include(GovukPublishingComponentsSkipSlimmer)
+
+class ComponentGuideTest < ActionDispatch::IntegrationTest
+  include Slimmer::TestHelpers::GovukComponents
+
+  def setup
+    stub_shared_component_locales
+  end
+
+  context "component guide" do
+    should "render an index" do
+      visit "/component-guide"
+      assert page.has_selector? "title", text: 'Static Component Guide', visible: false
+      assert page.has_selector? shared_component_selector('title')
+    end
+
+    should "render all component previews without erroring" do
+      visit '/component-guide'
+      all(:css, '.component-list a').map { |el| "#{el[:href]}/preview" }.each { |component| visit component }
+    end
+  end
+end