Load lazy route set before inserting test routes

Without loading lazy route sets, we miss after route load calbacks, or
risk invoking thme with the test routes instead of the real ones.

Author: gmcgibbon

actionpack/lib/action_dispatch/testing/assertions/routing.rb

@@ -25,7 +25,7 @@ def with_routing(&block)
             old_integration_session = nil
 
             setup do
-              old_routes = app.routes
+              old_routes = initialize_lazy_routes(app.routes)
               old_routes_call_method = old_routes.method(:call)
               old_integration_session = integration_session
               create_routes(&block)
@@ -38,7 +38,7 @@ def with_routing(&block)
         end
 
         def with_routing(&block)
-          old_routes = app.routes
+          old_routes = initialize_lazy_routes(app.routes)
           old_routes_call_method = old_routes.method(:call)
           old_integration_session = integration_session
           create_routes(&block)
@@ -47,6 +47,14 @@ def with_routing(&block)
         end
 
         private
+          def initialize_lazy_routes(routes)
+            if defined?(Rails::Engine::LazyRouteSet) && routes.is_a?(Rails::Engine::LazyRouteSet)
+              routes.tap(&:routes)
+            else
+              routes
+            end
+          end
+
           def create_routes
             app = self.app
             routes = ActionDispatch::Routing::RouteSet.new

railties/test/application/integration_test_case_test.rb

@@ -72,5 +72,49 @@ def test_app_returns_action_dispatch_test_app_by_default
       output = rails("test")
       assert_match(/0 failures, 0 errors/, output)
     end
+
+    test "routes are loaded before inserting test routes" do
+      app_file "config/routes.rb", <<-RUBY
+        Rails.application.routes.draw do
+          get "/c", as: :c, to: "users#show"
+        end
+      RUBY
+
+      app_file "config/initializers/after_routes_loaded.rb", <<-RUBY
+        Rails.configuration.after_routes_loaded do
+          $after_routes_loaded = true
+        end
+      RUBY
+
+      app_file "app/controllers/users_controller.rb", <<-RUBY
+        class UsersController < ActionController::Base
+          def index
+            render json: { loaded: $after_routes_loaded }
+          end
+        end
+      RUBY
+
+      app_file "test/controllers/users_controller_test.rb", <<-RUBY
+        require "test_helper"
+
+        class UsersControllerTest < ActionDispatch::IntegrationTest
+          with_routing do |set|
+            set.draw do
+              resources(:users, only: :index)
+            end
+          end
+
+          test "lazy route loading" do
+            get("/users")
+
+            assert_equal({ "loaded" => true }, JSON.parse(response.body))
+          end
+        end
+      RUBY
+
+      output = rails("test")
+      assert_match(/0 failures, 0 errors/, output)
+    end
+
   end
 end