Test slugs from the user's point of view

System tests are about user experience, so instead of checking the slug
has been updated in the database, we check whether the page can be
accessed using the slug.

Note the budget group test is a bit different because the name of the
group isn't present in the budget group page.

spec/system/admin/poll/polls_spec.rb

@@ -75,7 +75,10 @@ describe "Admin polls", :admin do
     expect(page).to have_content "Upcoming poll"
     expect(page).to have_content I18n.l(start_date)
     expect(page).to have_content I18n.l(end_date)
-    expect(Poll.last.slug).to eq "#{Poll.last.name.to_s.parameterize}"
+
+    visit poll_path(id: "upcoming-poll")
+
+    expect(page).to have_content "Upcoming poll"
   end
 
   scenario "Edit" do