Refactor finish_retirement method for Service Retirement.

This PR is based on the issue below.
ManageIQ/manageiq#12038

@miq-bot add_label refactoring
@miq-bot assign @tinaafitz

Added test for retirement_state equal 'retired'
Changed to use a service method

content/automate/ManageIQ/Service/Retirement/StateMachines/Methods.class/__methods__/finish_retirement.rb

@@ -2,6 +2,41 @@
 # Description: This method marks the service as retired
 #
 
-service = $evm.root['service']
-service.finish_retirement if service
-$evm.create_notification(:type => :service_retired, :subject => service) if service
+module ManageIQ
+  module Automate
+    module Service
+      module Retirement
+        module StateMachines
+          module Methods
+            class FinishRetirement
+              def initialize(handle = $evm)
+                @handle = handle
+              end
+
+              def main
+                finish_retirement(service)
+              end
+
+              private
+
+              def service
+                @handle.root["service"].tap do |service| 
+                  @handle.log(:warn, "Service Object not found") if service.nil?
+                end
+              end
+
+              def finish_retirement(service)
+                if service
+                  service.finish_retirement
+                  @handle.create_notification(:type => :service_retired, :subject => service)
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end
+
+ManageIQ::Automate::Service::Retirement::StateMachines::Methods::FinishRetirement.new.main

spec/content/automate/ManageIQ/Service/Retirement/StateMachines/Methods.class/__methods__/finish_retirement_spec.rb

@@ -0,0 +1,29 @@
+require_domain_file
+
+describe ManageIQ::Automate::Service::Retirement::StateMachines::Methods::FinishRetirement do
+  let(:admin) { FactoryBot.create(:user_admin) }
+  let(:request) { FactoryBot.create(:service_retire_request, :requester => admin) }
+  let(:service) { FactoryBot.create(:service, 'retirement_state'    => 'retired') }
+  let(:task) { FactoryBot.create(:service_retire_task, :destination => service, :miq_request => request) }
+  let(:svc_task) { MiqAeMethodService::MiqAeServiceServiceRetireTask.find(task.id) }
+  let(:svc_service) { MiqAeMethodService::MiqAeServiceService.find(service.id) }
+  let(:root_object) do
+    Spec::Support::MiqAeMockObject.new('service'             => svc_service,
+                                       'service_retire_task' => svc_task,
+                                       'service_action'      => 'Retirement')
+  end
+  let(:ae_service) { Spec::Support::MiqAeMockService.new(root_object) }
+
+  it "without service" do
+    ae_service.root['service'] = nil
+    expect(ae_service).not_to receive(:create_notification)
+    expect { described_class.new(ae_service).main }.not_to raise_error
+  end
+
+  it "retires vm" do
+    expect(svc_service).to receive(:finish_retirement)
+    expect(ae_service).to receive(:create_notification).with(:type => :service_retired, :subject => svc_service)
+    described_class.new(ae_service).main
+    expect(service.retirement_state).to eq("retired")
+  end
+end