Reorder Email Handlers based on email traffic pattern

This change reorders email handlers based on
email traffic patterns observed on .com

ee/lib/ee/gitlab/email/handler.rb

@@ -12,8 +12,8 @@ module EE
           override :load_handlers
           def load_handlers
             [
-              ::Gitlab::Email::Handler::EE::ServiceDeskHandler,
-              *super
+              *super,
+              ::Gitlab::Email::Handler::EE::ServiceDeskHandler
             ]
           end
         end

lib/gitlab/email/handler.rb

@@ -9,10 +9,10 @@ module Gitlab
 
       def self.load_handlers
         [
-          UnsubscribeHandler,
           CreateNoteHandler,
-          CreateMergeRequestHandler,
-          CreateIssueHandler
+          CreateIssueHandler,
+          UnsubscribeHandler,
+          CreateMergeRequestHandler
         ]
       end
 

spec/lib/gitlab/email/handler_spec.rb

@@ -6,6 +6,18 @@ describe Gitlab::Email::Handler do
   let(:email) { Mail.new { body 'email' } }
 
   describe '.for' do
+    context 'key matches the reply_key of a notification' do
+      it 'picks note handler' do
+        expect(described_class.for(email, '1234567890abcdef1234567890abcdef')).to be_an_instance_of(Gitlab::Email::Handler::CreateNoteHandler)
+      end
+    end
+
+    context 'key matches the reply_key of a notification, along with an unsubscribe suffix' do
+      it 'picks unsubscribe handler' do
+        expect(described_class.for(email, '1234567890abcdef1234567890abcdef-unsubscribe')).to be_an_instance_of(Gitlab::Email::Handler::UnsubscribeHandler)
+      end
+    end
+
     it 'picks issue handler if there is no merge request prefix' do
       expect(described_class.for(email, 'project+key')).to be_an_instance_of(Gitlab::Email::Handler::CreateIssueHandler)
     end