ActionMailer::Base can unregister observer(s) and interceptor(s). (#32207)

* ActionMailer::Base can unregister observer(s) and interceptor(s).

One or multiple mail observers can be unregistered using
`ActionMailer::Base.unregister_observers` or
`ActionMailer::Base.unregister_observer`.

One or multiple mail interceptors can be unregistered using
`ActionMailer::Base.unregister_interceptors` or
`ActionMailer::Base.unregister_interceptor`.

For preview interceptors, it's possible to use
`ActionMailer::Base.unregister_preview_interceptors` or
`ActionMailer::Base.unregister_preview_interceptor`.

* Ensure to be reset registered observer(s) and interceptor(s)

* Add explanation to CHANGELOG

* Add original author's name

[Kota Miyake + Rafael Mendonça França + Claudio Ortolina]

1 files changed, 22 insertions, 5 deletions

diff --git a/actionmailer/lib/action_mailer/preview.rb b/actionmailer/lib/action_mailer/preview.rb
index 0aea84fd2b..500b3bede0 100644
--- a/actionmailer/lib/action_mailer/preview.rb
+++ b/actionmailer/lib/action_mailer/preview.rb
@@ -31,22 +31,39 @@ module ActionMailer
         interceptors.flatten.compact.each { |interceptor| register_preview_interceptor(interceptor) }
       end
 
+      # Unregister one or more previously registered Interceptors.
+      def unregister_preview_interceptors(*interceptors)
+        interceptors.flatten.compact.each { |interceptor| unregister_preview_interceptor(interceptor) }
+      end
+
       # Register an Interceptor which will be called before mail is previewed.
       # Either a class or a string can be passed in as the Interceptor. If a
       # string is passed in it will be constantized.
       def register_preview_interceptor(interceptor)
-        preview_interceptor = \
+        preview_interceptor = interceptor_class_for(interceptor)
+
+        unless preview_interceptors.include?(preview_interceptor)
+          preview_interceptors << preview_interceptor
+        end
+      end
+
+      # Unregister a previously registered Interceptor.
+      # Either a class or a string can be passed in as the Interceptor. If a
+      # string is passed in it will be constantized.
+      def unregister_preview_interceptor(interceptor)
+        preview_interceptors.delete(interceptor_class_for(interceptor))
+      end
+
+      private
+
+        def interceptor_class_for(interceptor)
           case interceptor
           when String, Symbol
             interceptor.to_s.camelize.constantize
           else
             interceptor
           end
-
-        unless preview_interceptors.include?(preview_interceptor)
-          preview_interceptors << preview_interceptor
         end
-      end
     end
   end