3 files changed, 22 insertions, 5 deletions
diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index bb3cb1be45..4259eb0bee 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -664,7 +664,7 @@ module ActionMailer
     #
     # You can also specify overrides if you want by passing a hash instead of a string:
     #
-    #  mail.attachments['filename.jpg'] = {mime_type: 'application/x-gzip',
+    #  mail.attachments['filename.jpg'] = {mime_type: 'application/gzip',
     #                                      content: File.read('/path/to/filename.jpg')}
     #
     # If you want to use encoding other than Base64 then you will need to pass encoding
@@ -672,7 +672,7 @@ module ActionMailer
     # data:
     #
     #  file_content = SpecialEncode(File.read('/path/to/filename.jpg'))
-    #  mail.attachments['filename.jpg'] = {mime_type: 'application/x-gzip',
+    #  mail.attachments['filename.jpg'] = {mime_type: 'application/gzip',
     #                                      encoding: 'SpecialEncoding',
     #                                      content: file_content }
     #
diff --git a/actionmailer/lib/action_mailer/railtie.rb b/actionmailer/lib/action_mailer/railtie.rb
index fa707021c7..6a633e4ce8 100644
--- a/actionmailer/lib/action_mailer/railtie.rb
+++ b/actionmailer/lib/action_mailer/railtie.rb
@@ -47,10 +47,12 @@ module ActionMailer
 
         if options.show_previews
           app.routes.prepend do
-            get '/rails/mailers'         => "rails/mailers#index"
-            get '/rails/mailers/*path'   => "rails/mailers#preview"
+            get '/rails/mailers'         => "rails/mailers#index", internal: true
+            get '/rails/mailers/*path'   => "rails/mailers#preview", internal: true
           end
         end
+
+        ActionDispatch::IntegrationTest.send :include, ActionMailer::TestCase::ClearTestDeliveries
       end
     end
 
diff --git a/actionmailer/lib/action_mailer/test_case.rb b/actionmailer/lib/action_mailer/test_case.rb
index 0aa15e31ba..d83719e57d 100644
--- a/actionmailer/lib/action_mailer/test_case.rb
+++ b/actionmailer/lib/action_mailer/test_case.rb
@@ -11,6 +11,21 @@ module ActionMailer
   end
 
   class TestCase < ActiveSupport::TestCase
+    module ClearTestDeliveries
+      extend ActiveSupport::Concern
+
+      included do
+        teardown :clear_test_deliviers
+      end
+
+      private
+      def clear_test_deliviers
+        if ActionMailer::Base.delivery_method == :test
+          ActionMailer::Base.deliveries.clear
+        end
+      end
+    end
+
     module Behavior
       extend ActiveSupport::Concern
 
@@ -66,7 +81,6 @@ module ActionMailer
         def restore_test_deliveries # :nodoc:
           restore_delivery_method
           ActionMailer::Base.perform_deliveries = @old_perform_deliveries
-          ActionMailer::Base.deliveries.clear
         end
 
         def set_delivery_method(method) # :nodoc:
@@ -100,5 +114,6 @@ module ActionMailer
     end
 
     include Behavior
+    include ClearTestDeliveries
   end
 end