Extract issuable severity update into a service

Extract Issuable#severity_update into
IncidentManagement::Incidents::UpdateSeverityService class

app/models/concerns/issuable.rb

@@ -203,15 +203,6 @@ module Issuable
       issuable_severity&.severity || IssuableSeverity::DEFAULT
     end
 
-    def update_severity(severity)
-      return unless incident?
-
-      severity = severity.to_s.downcase
-      severity = IssuableSeverity::DEFAULT unless IssuableSeverity.severities.key?(severity)
-
-      (issuable_severity || build_issuable_severity(issue_id: id)).update(severity: severity)
-    end
-
     private
 
     def description_max_length_for_new_records_is_valid

app/services/incident_management/incidents/create_service.rb

@@ -24,7 +24,7 @@ module IncidentManagement
 
         return error(issue.errors.full_messages.to_sentence, issue) unless issue.valid?
 
-        issue.update_severity(severity)
+        update_severity_for(issue)
 
         success(issue)
       end
@@ -40,6 +40,10 @@ module IncidentManagement
       def error(message, issue = nil)
         ServiceResponse.error(payload: { issue: issue }, message: message)
       end
+
+      def update_severity_for(issue)
+        ::IncidentManagement::Incidents::UpdateSeverityService.new(issue, current_user, severity).execute
+      end
     end
   end
 end

app/services/incident_management/incidents/update_severity_service.rb

+# frozen_string_literal: true
+
+module IncidentManagement
+  module Incidents
+    class UpdateSeverityService < BaseService
+      def initialize(issuable, current_user, severity)
+        super(issuable.project, current_user)
+
+        @issuable = issuable
+        @severity = severity.to_s.downcase
+        @severity = IssuableSeverity::DEFAULT unless IssuableSeverity.severities.key?(@severity)
+      end
+
+      def execute
+        return unless issuable.incident?
+
+        issuable_severity.update(severity: severity)
+      end
+
+      private
+
+      attr_reader :issuable, :severity
+
+      def issuable_severity
+        issuable.issuable_severity || issuable.build_issuable_severity(issue_id: issuable.id)
+      end
+    end
+  end
+end

app/services/issuable_base_service.rb

@@ -321,7 +321,7 @@ class IssuableBaseService < BaseService
 
   def change_severity(issuable)
     if severity = params.delete(:severity)
-      issuable.update_severity(severity)
+      ::IncidentManagement::Incidents::UpdateSeverityService.new(issuable, current_user, severity).execute
     end
   end
 

spec/models/concerns/issuable_spec.rb

@@ -926,58 +926,4 @@ RSpec.describe Issuable do
       end
     end
   end
-
-  describe '#update_severity' do
-    let(:severity) { 'low' }
-
-    subject(:update_severity) { issuable.update_severity(severity) }
-
-    context 'when issuable not an incident' do
-      %i(issue merge_request).each do |issuable_type|
-        let(:issuable) { build_stubbed(issuable_type) }
-
-        it { is_expected.to be_nil }
-
-        it 'does not set severity' do
-          expect { subject }.not_to change(IssuableSeverity, :count)
-        end
-      end
-    end
-
-    context 'when issuable is an incident' do
-      let!(:issuable) { create(:incident) }
-
-      context 'when issuable does not have issuable severity yet' do
-        it 'creates new record' do
-          expect { update_severity }.to change { IssuableSeverity.where(issue: issuable).count }.to(1)
-        end
-
-        it 'sets severity to specified value' do
-          expect { update_severity }.to change { issuable.severity }.to('low')
-        end
-      end
-
-      context 'when issuable has an issuable severity' do
-        let!(:issuable_severity) { create(:issuable_severity, issue: issuable, severity: 'medium') }
-
-        it 'does not create new record' do
-          expect { update_severity }.not_to change(IssuableSeverity, :count)
-        end
-
-        it 'updates existing issuable severity' do
-          expect { update_severity }.to change { issuable_severity.severity }.to(severity)
-        end
-      end
-
-      context 'when severity value is unsupported' do
-        let(:severity) { 'unsupported-severity' }
-
-        it 'sets the severity to default value' do
-          update_severity
-
-          expect(issuable.issuable_severity.severity).to eq(IssuableSeverity::DEFAULT)
-        end
-      end
-    end
-  end
 end

spec/services/incident_management/incidents/update_severity_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe IncidentManagement::Incidents::UpdateSeverityService do
+  let_it_be(:user) { create(:user) }
+
+  describe '#execute' do
+    let(:severity) { 'low' }
+
+    subject(:update_severity) { described_class.new(issuable, user, severity).execute }
+
+    context 'when issuable not an incident' do
+      %i(issue merge_request).each do |issuable_type|
+        let(:issuable) { build_stubbed(issuable_type) }
+
+        it { is_expected.to be_nil }
+
+        it 'does not set severity' do
+          expect { subject }.not_to change(IssuableSeverity, :count)
+        end
+      end
+    end
+
+    context 'when issuable is an incident' do
+      let!(:issuable) { create(:incident) }
+
+      context 'when issuable does not have issuable severity yet' do
+        it 'creates new record' do
+          expect { update_severity }.to change { IssuableSeverity.where(issue: issuable).count }.to(1)
+        end
+
+        it 'sets severity to specified value' do
+          expect { update_severity }.to change { issuable.severity }.to('low')
+        end
+      end
+
+      context 'when issuable has an issuable severity' do
+        let!(:issuable_severity) { create(:issuable_severity, issue: issuable, severity: 'medium') }
+
+        it 'does not create new record' do
+          expect { update_severity }.not_to change(IssuableSeverity, :count)
+        end
+
+        it 'updates existing issuable severity' do
+          expect { update_severity }.to change { issuable_severity.severity }.to(severity)
+        end
+      end
+
+      context 'when severity value is unsupported' do
+        let(:severity) { 'unsupported-severity' }
+
+        it 'sets the severity to default value' do
+          update_severity
+
+          expect(issuable.issuable_severity.severity).to eq(IssuableSeverity::DEFAULT)
+        end
+      end
+    end
+  end
+end