Use system specs instead of feature specs

We get rid of database cleaner, and JavaScript tests are faster because
between tests we now rollback transactions instead of truncating the
database.

spec/system/admin/poll/questions/answers/documents/documents_spec.rb

@@ -0,0 +1,40 @@
+require "rails_helper"
+
+describe "Documents" do
+  before do
+    admin = create(:administrator)
+    login_as(admin.user)
+  end
+
+  context "Index" do
+    scenario "Answer with no documents" do
+      answer = create(:poll_question_answer)
+      document = create(:document)
+
+      visit admin_answer_documents_path(answer)
+
+      expect(page).not_to have_content(document.title)
+    end
+
+    scenario "Answer with documents" do
+      answer = create(:poll_question_answer)
+      document = create(:document, documentable: answer)
+
+      visit admin_answer_documents_path(answer)
+
+      expect(page).to have_content(document.title)
+    end
+  end
+
+  scenario "Remove document from answer", :js do
+    answer = create(:poll_question_answer)
+    document = create(:document, documentable: answer)
+
+    visit admin_answer_documents_path(answer)
+    expect(page).to have_content(document.title)
+
+    accept_confirm { click_link "Delete" }
+
+    expect(page).not_to have_content(document.title)
+  end
+end