no reason to lazily instantiate the routes

especially if you're just going to add a call two lines down that
populates the cache. common.

actionpack/test/dispatch/prefix_generation_test.rb

@@ -25,9 +25,7 @@ class WithMountedEngine < ActionDispatch::IntegrationTest
     include Rack::Test::Methods
 
     class BlogEngine < Rails::Engine
-      def self.routes
-        @routes ||= begin
-          routes = ActionDispatch::Routing::RouteSet.new
+      @routes = ActionDispatch::Routing::RouteSet.new.tap { |routes|
         routes.draw do
           get "/posts/:id", :to => "inside_engine_generating#show", :as => :post
           get "/posts", :to => "inside_engine_generating#index", :as => :posts
@@ -50,9 +48,10 @@ def self.routes
           get "/absolute_custom_root",     :to => redirect { |params, request| "/" }
           get "/absolute_custom_redirect", :to => redirect { |params, request| "/foo" }
         end
+      }
 
-          routes
-        end
+      def self.routes
+        @routes
       end
 
       def self.call(env)
@@ -62,9 +61,7 @@ def self.call(env)
     end
 
     class RailsApplication
-      def self.routes
-        @routes ||= begin
-          routes = ActionDispatch::Routing::RouteSet.new
+      @routes = ActionDispatch::Routing::RouteSet.new.tap { |routes|
         routes.draw do
           scope "/:omg", :omg => "awesome" do
             mount BlogEngine => "/blog", :as => "blog_engine"
@@ -78,9 +75,10 @@ def self.routes
           get "/ivar_usage", :to => "outside_engine_generating#ivar_usage"
           root :to => "outside_engine_generating#index"
         end
+      }
 
-          routes
-        end
+      def self.routes
+        @routes
       end
 
       def self.call(env)
@@ -90,7 +88,6 @@ def self.call(env)
     end
 
     # force draw
-    RailsApplication.routes
     RailsApplication.routes.define_mounted_helper(:main_app)
 
     class ::InsideEngineGeneratingController < ActionController::Base