suggested changes that includes:

moving actions for custom domain in its own controller
use separate service class for custom domains
updated help text for custom domains
increased test coverage for custom domains

spec/controllers/admin/conference_domains_controller_spec.rb

@@ -0,0 +1,42 @@
+require 'spec_helper'
+
+describe Admin::ConferenceDomainsController do
+  let!(:admin) { create(:admin) }
+  let!(:conference) { create(:conference) }
+  context 'as signed in admin' do
+    before do
+      sign_in admin
+    end
+
+    describe 'GET #show' do
+      it 'redirects to edit if custom domain is not present' do
+        get :show, conference_id: conference.short_title
+        expect(response).to redirect_to(admin_conference_conference_domains_edit_path)
+      end
+
+      it 'renders correct template if custom domain is present' do
+        conference.update_attribute(:custom_domain, 'mydomain.conf')
+        get :show, conference_id: conference.short_title
+        expect(response).to render_template('show')
+      end
+    end
+
+    describe 'PATCH #update' do
+      before do
+        patch :update, conference_id: conference.short_title,
+                       conference: { custom_domain: 'newdomain.conf' }
+      end
+
+      it 'successfully updates the custom domain' do
+        expect(conference.reload.custom_domain).to eq('newdomain.conf')
+      end
+    end
+
+    describe 'GET #edit' do
+      it 'renders correct template' do
+        get :edit, conference_id: conference.short_title
+        expect(response).to render_template('edit')
+      end
+    end
+  end
+end