Load AV::Layout to AM::Base in railties

actionmailer/lib/action_mailer/base.rb

@@ -368,8 +368,6 @@ module ActionMailer
 
     include AbstractController::Rendering
 
-    include ActionView::Layouts
-
     include AbstractController::Logger
     include AbstractController::Helpers
     include AbstractController::Translation

actionmailer/test/abstract_unit.rb

@@ -13,6 +13,9 @@ require 'action_mailer'
 require 'action_mailer/test_case'
 require 'mail'
 
+# Emulate AV railtie
+ActionMailer::Base.send(:include, ActionView::Layouts)
+
 # Show backtraces for deprecated behavior for quicker cleanup.
 ActiveSupport::Deprecation.debug = true
 

actionmailer/test/i18n_with_controller_test.rb

@@ -1,4 +1,5 @@
 require 'abstract_unit'
+require 'action_view'
 require 'action_controller'
 
 class I18nTestMailer < ActionMailer::Base
@@ -14,6 +15,9 @@ class I18nTestMailer < ActionMailer::Base
   end
 end
 
+# Emulate AV railtie
+ActionController::Base.superclass.send(:include, ActionView::Layouts)
+
 class TestController < ActionController::Base
   def send_mail
     I18nTestMailer.mail_with_i18n_subject("test@localhost").deliver

actionpack/test/controller/assert_select_test.rb

@@ -8,6 +8,9 @@ require 'abstract_unit'
 require 'controller/fake_controllers'
 
 require 'action_mailer'
+require 'action_view'
+
+ActionMailer::Base.send(:include, ActionView::Layouts)
 ActionMailer::Base.view_paths = FIXTURE_LOAD_PATH
 
 class AssertSelectTest < ActionController::TestCase

actionview/lib/action_view/railtie.rb

@@ -41,5 +41,11 @@ module ActionView
         ActionController::Base.superclass.send(:include, ActionView::Layouts)
       end
     end
+
+    initializer "action_view.setup_action_mailer" do |app|
+      ActiveSupport.on_load(:action_mailer) do
+        ActionMailer::Base.send(:include, ActionView::Layouts)
+      end
+    end
   end
 end