Allow to use mounted helpers in ActionView::TestCase

Similarly to 65250022, this allows to use routes helpers for mounted
helpers, but this time in ActionView::TestCase

actionpack/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   Allow to use mounted_helpers (helpers for accessing mounted engines) in ActionView::TestCase. *Piotr Sarnacki*
+
 *   Include mounted_helpers (helpers for accessing mounted engines) in ActionDispatch::IntegrationTest by default. *Piotr Sarnacki*
 
 *   Extracted redirect logic from `ActionController::ForceSSL::ClassMethods.force_ssl`  into `ActionController::ForceSSL#force_ssl_redirect`

actionpack/lib/action_view/test_case.rb

@@ -229,7 +229,8 @@ def _routes
 
       def method_missing(selector, *args)
         if @controller.respond_to?(:_routes) &&
-          @controller._routes.named_routes.helpers.include?(selector)
+          ( @controller._routes.named_routes.helpers.include?(selector) ||
+            @controller._routes.mounted_helpers.method_defined?(selector) )
           @controller.__send__(selector, *args)
         else
           super

actionpack/test/abstract_unit.rb

@@ -277,6 +277,7 @@ class Base
     include ActionController::Testing
     # This stub emulates the Railtie including the URL helpers from a Rails application
     include SharedTestRoutes.url_helpers
+    include SharedTestRoutes.mounted_helpers
 
     self.view_paths = FIXTURE_LOAD_PATH
 

actionpack/test/template/test_case_test.rb

@@ -222,6 +222,25 @@ class ATestHelperTest < ActionView::TestCase
       end
     end
 
+    test "is able to use mounted routes" do
+      with_routing do |set|
+        app = Class.new do
+          def self.routes
+            @routes ||= ActionDispatch::Routing::RouteSet.new
+          end
+
+          routes.draw { get "bar", :to => lambda {} }
+
+          def self.call(*)
+          end
+        end
+
+        set.draw { mount app => "/foo", :as => "foo_app" }
+
+        assert_equal '/foo/bar', foo_app.bar_path
+      end
+    end
+
     test "named routes can be used from helper included in view" do
       with_routing do |set|
         set.draw { resources :contents }