Merge pull request #24086 from yui-knk/do_not_ad_integration_test_class

Prevent not-intended loading of `ActionDispatch::IntegrationTest`

actionmailer/lib/action_mailer/railtie.rb

@@ -45,9 +45,9 @@ module ActionMailer
         register_observers(options.delete(:observers))
 
         options.each { |k,v| send("#{k}=", v) }
-
-        ActionDispatch::IntegrationTest.send :include, ActionMailer::TestCase::ClearTestDeliveries
       end
+
+      ActiveSupport.on_load(:action_dispatch_integration_test) { include ActionMailer::TestCase::ClearTestDeliveries }
     end
 
     initializer "action_mailer.compile_config_methods" do

actionpack/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Add `action_dispatch_integration_test` load hook. The hook can be used to
+    extend `ActionDispatch::IntegrationTest` once it has been loaded.
+
+    *Yuichiro Kaneko*
+
 *   Update default rendering policies when the controller action did
     not explicitly indicate a response.
 

actionpack/lib/action_dispatch/testing/integration.rb

@@ -764,5 +764,7 @@ module ActionDispatch
     def self.register_encoder(*args)
       Integration::Session::RequestEncoder.register_encoder(*args)
     end
+
+    ActiveSupport.run_load_hooks(:action_dispatch_integration_test, self)
   end
 end