add a spec for ServiceDeskHandler

spec/fixtures/emails/service_desk.eml

+Return-Path: <jake@adventuretime.ooo>
+Received: from iceking.adventuretime.ooo ([unix socket]) by iceking (Cyrus v2.2.13-Debian-2.2.13-19+squeeze3) with LMTPA; Thu, 13 Jun 2013 17:03:50 -0400
+Received: from mail-ie0-x234.google.com (mail-ie0-x234.google.com [IPv6:2607:f8b0:4001:c03::234]) by iceking.adventuretime.ooo (8.14.3/8.14.3/Debian-9.4) with ESMTP id r5DL3nFJ016967 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=NOT) for <incoming+gitlabhq/gitlabhq@appmail.adventuretime.ooo>; Thu, 13 Jun 2013 17:03:50 -0400
+Received: by mail-ie0-f180.google.com with SMTP id f4so21977375iea.25 for <incoming+gitlabhq/gitlabhq@appmail.adventuretime.ooo>; Thu, 13 Jun 2013 14:03:48 -0700
+Received: by 10.0.0.1 with HTTP; Thu, 13 Jun 2013 14:03:48 -0700
+Date: Thu, 13 Jun 2013 17:03:48 -0400
+From: Jake the Dog <jake@adventuretime.ooo>
+To: incoming+service-desk+somemailkey@appmail.adventuretime.ooo
+Message-ID: <CADkmRc+rNGAGGbV2iE5p918UVy4UyJqVcXRO2=otppgzduJSg@mail.gmail.com>
+Subject: The message subject! @all
+Mime-Version: 1.0
+Content-Type: text/plain;
+ charset=ISO-8859-1
+Content-Transfer-Encoding: 7bit
+X-Sieve: CMU Sieve 2.2
+X-Received: by 10.0.0.1 with SMTP id n7mr11234144ipb.85.1371157428600; Thu,
+ 13 Jun 2013 14:03:48 -0700 (PDT)
+X-Scanned-By: MIMEDefang 2.69 on IPv6:2001:470:1d:165::1
+
+Service desk stuff!
+
+```
+a = b
+```

spec/lib/gitlab/email/handler/service_desk_handler_spec.rb

+require 'spec_helper'
+require_relative '../email_shared_blocks'
+
+describe Gitlab::Email::Handler::EE::ServiceDeskHandler do
+  include_context :email_shared_context
+  before do
+    stub_incoming_email_setting(enabled: true, address: "incoming+%{key}@appmail.adventuretime.ooo")
+    stub_config_setting(host: 'localhost')
+  end
+
+  let(:email_raw) { fixture_file('emails/service_desk.eml') }
+  let(:project) { create(:project, :public) }
+
+  context 'when service desk is enabled' do
+    before do
+      project.update_attributes(
+        service_desk_enabled: true,
+        service_desk_mail_key: 'somemailkey',
+      )
+    end
+
+    it 'receives the email', jneen: true do
+      setup_attachment
+
+      expect(Notify).to receive(:thank_you_email).with(instance_of(Fixnum))
+
+      expect { receiver.execute }.to change { Issue.count }.by(1)
+
+      new_issue = Issue.last
+
+      expect(new_issue.author).to eql(User.support_bot)
+      expect(new_issue.confidential?).to be true
+      expect(new_issue.all_references.all).to be_empty
+    end
+  end
+end