use deliver_now if possible in preparation for Rails 5

lib/devise/async/backend/base.rb

@@ -13,14 +13,26 @@ def self.enqueue(*args)
         def perform(method, resource_class, resource_id, *args)
           resource = resource_class.constantize.to_adapter.get!(resource_id)
           args[-1] = args.last.symbolize_keys if args.last.is_a?(Hash)
-          mailer_class(resource).send(method, resource, *args).deliver
+          mailer = mailer_class(resource).send(method, resource, *args)
+          mailer.send(deliver_method(mailer))
         end
 
         private
 
         def mailer_class(resource = nil)
           @mailer_class ||= resource.try(:devise_mailer) || Devise.mailer
         end
+
+        # Use #deliver_now if supported, otherwise falls back to #deliver.
+        # Added in preparation for the planned removal of #deliver in Rails 5.
+        def deliver_method(mailer)
+          if mailer.respond_to?(:deliver_now)
+            :deliver_now
+          else
+            :deliver
+          end
+        end
+
       end
     end
   end

test/devise/async/backend/base_test.rb

@@ -22,6 +22,27 @@ module Backend
           Base.new.perform(:confirmation_instructions, "UserWithMailer", user.id, {})
         end
 
+        describe "the delivery method" do
+          before do
+            Devise.mailer = "MyMailer"
+            @user = create_user
+          end
+
+          it "uses #deliver_now when possible" do
+            mailer_instance = mock(:deliver_now => true)
+
+            MyMailer.expects(:confirmation_instructions).once.returns(mailer_instance)
+            Base.new.perform(:confirmation_instructions, "User", @user.id, {})
+          end
+
+          it "uses #deliver otherwise" do
+            mailer_instance = mock(:deliver => true)
+
+            MyMailer.expects(:confirmation_instructions).once.returns(mailer_instance)
+            Base.new.perform(:confirmation_instructions, "User", @user.id, {})
+          end
+        end
+
         after do
           Devise.mailer = "Devise::Mailer"
         end