メインアプリケーションとgem（マウント可能なエンジン）に同じクラスがあります。
gem でクラス (メイン アプリケーションで定義) を再度開きたい。
メインアプリケーションには
app/models/test.rbがあります
クラステスト def original_method 終わり 終わり
Gemfileで
宝石「gem_name」
gem
app/models/test.rb で
クラステスト def add_method 終わり 終わり
しかし、メインアプリケーションは Test#original_method が定義されていないというエラーを発生させます。
gem で Test クラスが上書きされているようです。なぜ再開しないのですか？
どうすれば問題を解決できますか??
編集
NoMethodError (undefined method `original_method' for #<Test:0x0000001997ca70>):
vendor/bundle/ruby/1.9.1/gems/activemodel-3.2.13/lib/active_model/attribute_methods.rb:407:in `method_missing'
vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.13/lib/active_record/attribute_methods.rb:149:in `method_missing'
vendor/bundle/ruby/1.9.1/bundler/gems/test_gem/app/controllers/tests_controller.rb:213:in `new'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/implicit_render.rb:4:in `send_action'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/abstract_controller/base.rb:167:in `process_action'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/rendering.rb:10:in `process_action'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/abstract_controller/callbacks.rb:18:in `block in process_action'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:535:in `_run__422315203817736318__process_action__439125674649202736__callbacks'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:405:in `__run_callback'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:81:in `run_callbacks'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/abstract_controller/callbacks.rb:17:in `process_action'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/rescue.rb:29:in `process_action'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/notifications.rb:123:in `block in instrument'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/notifications.rb:123:in `instrument'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/instrumentation.rb:29:in `process_action'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/params_wrapper.rb:207:in `process_action'
vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.13/lib/active_record/railties/controller_runtime.rb:18:in `process_action'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/abstract_controller/base.rb:121:in `process'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/abstract_controller/rendering.rb:45:in `process'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal.rb:203:in `dispatch'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal.rb:246:in `block in action'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/routing/route_set.rb:73:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/routing/route_set.rb:36:in `call'
vendor/bundle/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:68:in `block in call'
vendor/bundle/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:56:in `each'
vendor/bundle/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:56:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/routing/route_set.rb:612:in `call'
vendor/bundle/ruby/1.9.1/gems/warden-1.2.1/lib/warden/manager.rb:35:in `block in call'
vendor/bundle/ruby/1.9.1/gems/warden-1.2.1/lib/warden/manager.rb:34:in `catch'
vendor/bundle/ruby/1.9.1/gems/warden-1.2.1/lib/warden/manager.rb:34:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/etag.rb:23:in `call'
vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/conditionalget.rb:25:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/head.rb:14:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/params_parser.rb:21:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/flash.rb:242:in `call'
vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/session/abstract/id.rb:210:in `context'
vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/session/abstract/id.rb:205:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/cookies.rb:341:in `call'
vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.13/lib/active_record/query_cache.rb:64:in `call'
vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.13/lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:405:in `_run__4226710667851682500__call__4227166089575601802__callbacks'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:405:in `__run_callback'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:81:in `run_callbacks'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/callbacks.rb:27:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/reloader.rb:65:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/rack/logger.rb:32:in `call_app'
vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/rack/logger.rb:16:in `block in call'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/tagged_logging.rb:22:in `tagged'
vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/rack/logger.rb:16:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/request_id.rb:22:in `call'
vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/methodoverride.rb:21:in `call'
vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/runtime.rb:17:in `call'
vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/cache/strategy/local_cache.rb:72:in `call'
vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/lock.rb:15:in `call'
vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/static.rb:63:in `call'
vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/engine.rb:479:in `call'
vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/application.rb:223:in `call'
vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/content_length.rb:14:in `call'
vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/rack/log_tailer.rb:17:in `call'
vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/handler/webrick.rb:59:in `service'
/usr/local/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
/usr/local/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
/usr/local/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'