add spec for trying to create TOS with no file

spec/controllers/admin/terms_of_service_files_controller_spec.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Admin::TermsOfServiceFilesController, type: :controller do
+  let(:user) { create(:admin_user) }
+
+  before do
+    allow(controller).to receive(:spree_current_user) { user }
+  end
+
+  describe "trying to create terms of service without a file" do
+    it "redirects and show an error" do
+      post :create, params: {}
+      expect(response).to redirect_to admin_terms_of_service_files_path
+      expect(flash[:error]).to eq I18n.t(".admin.terms_of_service_files.create.select_file")
+    end
+  end
+end