Use singular route

Even simpler

app/controllers/admin/emails_controller.rb

 class Admin::EmailsController < Admin::ApplicationController
-  def index
-    render text: 'hello world', layout: nil
+  def show
+    render text: 'hello world'
   end
 end

config/routes.rb

@@ -86,7 +86,7 @@ Gitlab::Application.routes.draw do
     resources :broadcast_messages, only: [:index, :create, :destroy]
     resource :logs, only: [:show]
     resource :background_jobs, controller: 'background_jobs', only: [:show]
-    resources :emails, only: [:index]
+    resource :email, only: [:show]
 
     resources :projects, constraints: { id: /[a-zA-Z.\/0-9_\-]+/ }, only: [:index, :show] do
       member do

features/steps/shared/paths.rb

@@ -170,7 +170,7 @@ module SharedPaths
   end
 
   step 'I visit admin email page' do
-    visit admin_emails_path
+    visit admin_email_path
   end
   # ----------------------------------------
   # Generic Project

spec/routing/admin_routing_spec.rb

@@ -120,7 +120,7 @@ describe Admin::DashboardController, "routing" do
 end
 
 describe Admin::EmailsController, "routing" do
-  it "to #index" do
-    get("/admin/emails").should route_to('admin/emails#index')
+  it "to #show" do
+    get("/admin/email").should route_to('admin/emails#show')
   end
 end