Add notification to the former assignee upon unassignment

CHANGELOG

@@ -26,6 +26,7 @@ v 8.2.0 (unreleased)
   - Add "added", "modified" and "removed" properties to commit object in webhook
   - Rename "Back to" links to "Go to" because its not always a case it point to place user come from
   - Allow groups to appear in the search results if the group owner allows it
+  - Add email notification to former assignee upon unassignment
 v 8.1.3
   - Spread out runner contacted_at updates

app/services/notification_service.rb

@@ -362,7 +362,8 @@ class NotificationService
   def reassign_resource_email(target, project, current_user, method)
     assignee_id_was = previous_record(target, "assignee_id")
-    recipients = build_recipients(target, project, current_user)
+    previous_assignee = User.find(assignee_id_was)
+    recipients = build_recipients(target, project, current_user, [previous_assignee])
     recipients.each do |recipient|
       mailer.send(method, recipient.id, target.id, assignee_id_was, current_user.id)
@@ -377,8 +378,9 @@ class NotificationService
     end
   end
-  def build_recipients(target, project, current_user)
+  def build_recipients(target, project, current_user, previous_records = nil )
     recipients = target.participants(current_user)
+    recipients.concat(previous_records).compact.uniq if previous_records
     recipients = add_project_watchers(recipients, project)
     recipients = reject_mention_users(recipients, project)

spec/services/issues/update_service_spec.rb

@@ -3,7 +3,7 @@ require 'spec_helper'
 describe Issues::UpdateService do
   let(:user) { create(:user) }
   let(:user2) { create(:user) }
-  let(:issue) { create(:issue, title: 'Old title') }
+  let(:issue) { create(:issue, title: 'Old title', assignee_id: user.id) }
   let(:label) { create(:label) }
   let(:project) { issue.project }
@@ -34,9 +34,11 @@ describe Issues::UpdateService do
       it { expect(@issue.labels.count).to eq(1) }
       it { expect(@issue.labels.first.title).to eq('Bug') }
-      it 'should send email to user2 about assign of new issue' do
-        email = ActionMailer::Base.deliveries.last
-        expect(email.to.first).to eq(user2.email)
+      it 'should send email to user2 about assign of new issue and email to user about issue unassignment' do
+        deliveries =  ActionMailer::Base.deliveries
+        email = deliveries.last
+        recipients = deliveries.map(&:to).uniq.flatten
+        expect(recipients.last(2)).to include(user.email,user2.email)
         expect(email.subject).to include(issue.title)
       end