3 files changed, 45 insertions, 12 deletions
diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index bb3cb1be45..559cd06d91 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -430,6 +430,7 @@ module ActionMailer
     include AbstractController::Translation
     include AbstractController::AssetPaths
     include AbstractController::Callbacks
+    include AbstractController::Caching
 
     include ActionView::Layouts
 
@@ -664,7 +665,7 @@ 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 +673,7 @@ 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 }
     #
@@ -947,6 +948,18 @@ module ActionMailer
       container.add_part(part)
     end
 
+    # This and #instrument_name is for caching instrument
+    def instrument_payload(key)
+      {
+        mailer: mailer_name,
+        key: key
+      }
+    end
+
+    def instrument_name
+      "action_mailer"
+    end
+
     ActiveSupport.run_load_hooks(:action_mailer, self)
   end
 end
diff --git a/actionmailer/lib/action_mailer/railtie.rb b/actionmailer/lib/action_mailer/railtie.rb
index fa707021c7..215d0199af 100644
--- a/actionmailer/lib/action_mailer/railtie.rb
+++ b/actionmailer/lib/action_mailer/railtie.rb
@@ -25,6 +25,7 @@ module ActionMailer
       options.javascripts_dir ||= paths["public/javascripts"].first
       options.stylesheets_dir ||= paths["public/stylesheets"].first
       options.show_previews = Rails.env.development? if options.show_previews.nil?
+      options.cache_store ||= Rails.cache
 
       if options.show_previews
         options.preview_path  ||= defined?(Rails.root) ? "#{Rails.root}/test/mailers/previews" : nil
@@ -45,12 +46,7 @@ module ActionMailer
 
         options.each { |k,v| send("#{k}=", v) }
 
-        if options.show_previews
-          app.routes.prepend do
-            get '/rails/mailers'         => "rails/mailers#index"
-            get '/rails/mailers/*path'   => "rails/mailers#preview"
-          end
-        end
+        ActionDispatch::IntegrationTest.send :include, ActionMailer::TestCase::ClearTestDeliveries
       end
     end
 
@@ -60,9 +56,18 @@ module ActionMailer
       end
     end
 
-    config.after_initialize do
-      if ActionMailer::Base.preview_path
-        ActiveSupport::Dependencies.autoload_paths << ActionMailer::Base.preview_path
+    config.after_initialize do |app|
+      options = app.config.action_mailer
+
+      if options.show_previews
+        app.routes.prepend do
+          get '/rails/mailers'         => "rails/mailers#index", internal: true
+          get '/rails/mailers/*path'   => "rails/mailers#preview", internal: true
+        end
+
+        if options.preview_path
+          ActiveSupport::Dependencies.autoload_paths << options.preview_path
+        end
       end
     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