Refactor sending Prometheus alert mails

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

@@ -20,26 +20,21 @@ module EE
              subject: subject('Mirror user changed'))
       end
 
-      # rubocop: disable CodeReuse/ActiveRecord
       def prometheus_alert_fired_email(project_id, user_id, alert_params)
-        alert_metric_id = alert_params["labels"]["gitlab_alert_id"]
+        alert_metric_id = alert_params.dig('labels', 'gitlab_alert_id')
 
-        @project = ::Project.find_by(id: project_id)
-        return unless @project
+        @project = ::Project.find(project_id)
+        user = ::User.find(user_id)
 
-        @alert = @project.prometheus_alerts.find_by(prometheus_metric: alert_metric_id)
+        @alert = @project.prometheus_alerts.for_metric(alert_metric_id).first
         return unless @alert
 
         @environment = @alert.environment
 
-        user = ::User.find_by(id: user_id)
-        return unless user
-
         subject_text = "Alert: #{@environment.name} - #{@alert.title} #{@alert.computed_operator} #{@alert.threshold} for 5 minutes"
 
         mail(to: user.notification_email, subject: subject(subject_text))
       end
-      # rubocop: enable CodeReuse/ActiveRecord
     end
   end
 end

ee/spec/mailers/ee/emails/projects_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require 'email_spec'
+
+describe EE::Emails::Projects do
+  include EmailSpec::Matchers
+  include_context 'gitlab email notification'
+
+  shared_examples 'no email' do
+    it 'does not send mail' do
+      expect(subject.message).to be_a_kind_of(ActionMailer::Base::NullMail)
+    end
+  end
+
+  set(:user) { create(:user) }
+
+  describe '#prometheus_alert_fired_email' do
+    subject do
+      Notify.prometheus_alert_fired_email(project.id, user.id, alert_params)
+    end
+
+    context 'with an alert' do
+      let(:alert_params) do
+        {
+          'labels' => {
+            'gitlab_alert_id' => alert.prometheus_metric_id.to_s
+          }
+        }
+      end
+
+      let(:environment) { alert.environment }
+
+      let(:metrics_url) do
+        metrics_project_environment_url(project, environment)
+      end
+
+      let!(:alert) { create(:prometheus_alert, project: project) }
+
+      it_behaves_like 'an email sent from GitLab'
+      it_behaves_like 'it should not have Gmail Actions links'
+      it_behaves_like 'a user cannot unsubscribe through footer link'
+
+      it 'has expected subject' do
+        aggregate_failures do
+          is_expected.to have_subject(/Alert:/)
+          is_expected.to have_subject(/#{environment.name}/)
+
+          title = "#{alert.title} #{alert.computed_operator} #{alert.threshold}"
+          is_expected.to have_subject(/#{title}/)
+        end
+      end
+
+      it 'has expected content' do
+        is_expected.to have_body_text('An alert has been triggered')
+        is_expected.to have_body_text(project.full_path)
+        is_expected.to have_body_text(environment.name)
+        is_expected.to have_body_text(alert.full_query)
+        is_expected.to have_body_text(metrics_url)
+      end
+    end
+
+    context 'without an alert' do
+      let(:alert_params) { {} }
+
+      it_behaves_like 'no email'
+    end
+
+    context 'with an unknown alert' do
+      let(:alert_params) do
+        {
+          'labels' => {
+            'gitlab_alert_id' => 'unknown'
+          }
+        }
+      end
+
+      it_behaves_like 'no email'
+    end
+  end
+end