Don't allow to modify answer's documents for started polls

spec/controllers/documents_controller_spec.rb

@@ -0,0 +1,28 @@
+require "rails_helper"
+
+describe DocumentsController do
+  describe "DELETE destroy" do
+    context "Poll answers administration", :admin do
+      let(:current_answer) { create(:poll_question_answer, poll: create(:poll)) }
+      let(:future_answer) { create(:poll_question_answer, poll: create(:poll, :future)) }
+
+      it "is not possible for an already started poll" do
+        document = create(:document, documentable: current_answer)
+        delete :destroy, params: { id: document }
+
+        expect(flash[:alert]).to eq "You do not have permission to carry out the action 'destroy' on Document."
+        expect(Document.count).to eq 1
+      end
+
+      it "is possible for a not started poll" do
+        document = create(:document, documentable: future_answer)
+        request.env["HTTP_REFERER"] = admin_answer_documents_path(future_answer)
+        delete :destroy, params: { id: document }
+
+        expect(response).to redirect_to admin_answer_documents_path(future_answer)
+        expect(flash[:notice]).to eq "Document was deleted successfully."
+        expect(Document.count).to eq 0
+      end
+    end
+  end
+end