Add meta tags spec support and add to HelpPage spec

- test/integration/meta_tags_test.rb https://github.com/alphagov/government-frontend/blob/5d6622e384dcde9c19fcefe88d94414e1d6fb457/test/integration/meta_tags_test.rb

spec/support/meta_tags.rb

@@ -0,0 +1,20 @@
+RSpec.shared_examples "it has meta tags" do |schema, base_path|
+  before do
+    example_doc = GovukSchemas::RandomExample.for_schema(frontend_schema: schema) do |random|
+      random.merge!(
+        "title" => "Zhe title",
+        "withdrawn_notice" => {},
+      )
+      random["links"]["available_translations"] = []
+      random
+    end
+
+    stub_content_store_has_item("#{base_path}/some-page", example_doc.to_json)
+  end
+
+  it "renders the correct meta tags for the title" do
+    visit "#{base_path}/some-page"
+
+    expect(page).to have_css("meta[property='og:title'][content='Zhe title']", visible: false)
+  end
+end

spec/system/help_page_spec.rb

@@ -1,7 +1,9 @@
 RSpec.describe "HelpPage" do
+  it_behaves_like "it has meta tags", "help_page", "/help/about-govuk"
+
   before do
-    content_store_has_example_item("/help/about-govuk", schema: "help_page", example: "about-govuk")
-    content_store_has_example_item("/help/cookie-details", schema: "help_page", example: "cookie-details")
+    content_store_has_example_item("/help/about-govuk", schema: :help_page, example: "about-govuk")
+    content_store_has_example_item("/help/cookie-details", schema: :help_page, example: "cookie-details")
   end
 
   context "when visiting 'help/:slug'" do