Rails 4.2 support: when sending topic reply notifications use #delive…

…r_later if possible

app/models/forem/subscription.rb

@@ -9,7 +9,12 @@ def send_notification(post_id)
       # If a user cannot be found, then no-op
       # This will happen if the user record has been deleted.
       if subscriber.present?
-        SubscriptionMailer.topic_reply(post_id, subscriber.id).deliver
+        mail = SubscriptionMailer.topic_reply(post_id, subscriber.id)
+        if mail.respond_to?(:deliver_later)
+          mail.deliver_later
+        else
+          mail.deliver
+        end
       end
     end
   end

spec/models/subscription_spec.rb

@@ -32,5 +32,18 @@
       expect(Forem::SubscriptionMailer).not_to receive(:topic_reply)
       subscription.send_notification(1)
     end
+
+    it "should send a notification via deliver_later when method available" do
+      expect_any_instance_of(ActionMailer::MessageDelivery).to_not receive(:deliver)
+      expect_any_instance_of(ActionMailer::MessageDelivery).to receive(:deliver_later)
+      subscription.send_notification(1)
+    end
+
+    it "should send a notification via deliver when deliver_later not available" do
+      allow_any_instance_of(ActionMailer::MessageDelivery).to receive(:respond_to?).with(:deliver_later).and_return(false)
+      expect_any_instance_of(ActionMailer::MessageDelivery).to_not receive(:deliver_later)
+      expect_any_instance_of(ActionMailer::MessageDelivery).to receive(:deliver)
+      subscription.send_notification(1)
+    end
   end
 end