Fix image path in escalation email

Add specs for change in behaviour

ee/app/mailers/ee/emails/projects.rb

@@ -45,7 +45,6 @@ module EE
       def incident_escalation_fired_email(project, user, issue)
         @project = project
         @incident = issue.present
-
         @escalation_status = issue.incident_management_issuable_escalation_status
 
         add_project_headers

ee/app/models/issuable_metric_image.rb

@@ -33,7 +33,7 @@ class IssuableMetricImage < ApplicationRecord
       return file&.url unless file&.upload
 
       # If we're using a CDN, we need to use the full URL
-      asset_host = ActionController::Base.asset_host
+      asset_host = ActionController::Base.asset_host || Gitlab.config.gitlab.base_url
       local_path = Gitlab::Routing.url_helpers.issuable_metric_image_upload_path(
         filename: file.filename,
         id: file.upload.model_id,

ee/app/views/notify/incident_escalation_fired_email.html.haml

@@ -23,4 +23,4 @@
   %p
     = _('Metrics:')
     - @incident.metric_images.each do |image|
-      = link_to image.filename, image.url
+      = link_to image.filename, image.file_path

ee/app/views/notify/incident_escalation_fired_email.text.erb

@@ -12,3 +12,10 @@
 <% if @escalation_status.policy %>
 <%= _('Escalation policy:') %> <%= @escalation_status.policy.name %>
 <% end %>
+
+<% if @incident.metric_images.any? %>
+  <%= _('Metrics:') %>
+  <% @incident.metric_images.each do |image| %>
+    <%= image.file_path %>
+  <% end %>
+<% end %>

ee/spec/models/issuable_metric_image_spec.rb

@@ -60,4 +60,27 @@ RSpec.describe IssuableMetricImage do
       it { is_expected.to eq(false) }
     end
   end
+
+  describe '#file_path' do
+    let(:issuable_metric_image) { create(:issuable_metric_image) }
+    let(:expected_path) { issuable_metric_image.file.url }
+
+    subject(:file_path) { issuable_metric_image.file_path }
+
+    context 'with asset host configured' do
+      it 'returns a full URL with the asset host and system path' do
+        asset_host = 'https://gitlab-assets.example.com'
+        allow(ActionController::Base).to receive(:asset_host) { asset_host }
+
+        expect(file_path).to eq("#{asset_host}#{expected_path}")
+      end
+    end
+
+    context 'no asset path configured' do
+      it 'returns a full URL with the base url and system path' do
+        base_url = Gitlab.config.gitlab.base_url
+        expect(file_path).to eq("#{base_url}#{expected_path}")
+      end
+    end
+  end
 end