Fix the merge notification email not being sent

The 'author_id_of_changes' attribute is not persisted in the database.
As we retrieve the merge request from the DB just before sending the
email, this attribute was always nil.

Also there was no tests for the merge notification code - tests have
been added.

Fix #6605

app/mailers/emails/merge_requests.rb

@@ -29,11 +29,11 @@ module Emails
            subject: subject("#{@merge_request.title} (!#{@merge_request.iid})"))
     end
-    def merged_merge_request_email(recipient_id, merge_request_id)
+    def merged_merge_request_email(recipient_id, merge_request_id, updated_by_user_id)
       @merge_request = MergeRequest.find(merge_request_id)
       @project = @merge_request.project
       @target_url = project_merge_request_url(@project, @merge_request)
-      mail(from: sender(@merge_request.author_id_of_changes),
+      mail(from: sender(updated_by_user_id),
            to: recipient(recipient_id),
            subject: subject("#{@merge_request.title} (!#{@merge_request.iid})"))
     end

app/services/notification_service.rb

@@ -91,7 +91,7 @@ class NotificationService
     recipients = recipients.concat(project_watchers(merge_request.target_project)).uniq
     recipients.each do |recipient|
-      mailer.merged_merge_request_email(recipient.id, merge_request.id)
+      mailer.merged_merge_request_email(recipient.id, merge_request.id, merge_request.author_id_of_changes)
     end
   end

spec/mailers/notify_spec.rb

@@ -229,6 +229,7 @@ describe Notify do
       end
       context 'for merge requests' do
+        let(:merge_author) { create(:user) }
         let(:merge_request) { create(:merge_request, author: current_user, assignee: assignee, source_project: project, target_project: project) }
         let(:merge_request_with_description) { create(:merge_request, author: current_user, assignee: assignee, source_project: project, target_project: project, description: Faker::Lorem.sentence) }
@@ -288,7 +289,30 @@ describe Notify do
           it 'contains a link to the merge request' do
             should have_body_text /#{project_merge_request_path project, merge_request}/
           end
+        end
+
+        describe 'that are merged' do
+          subject { Notify.merged_merge_request_email(recipient.id, merge_request.id, merge_author.id) }
+
+          it_behaves_like 'a multiple recipients email'
+
+          it 'is sent as the merge author' do
+            sender = subject.header[:from].addrs[0]
+            sender.display_name.should eq(merge_author.name)
+            sender.address.should eq(gitlab_sender)
+          end
+
+          it 'has the correct subject' do
+            should have_subject /#{merge_request.title} \(!#{merge_request.iid}\)/
+          end
+          it 'contains the new status' do
+            should have_body_text /merged/i
+          end
+
+          it 'contains a link to the merge request' do
+            should have_body_text /#{project_merge_request_path project, merge_request}/
+          end
         end
       end
     end

spec/services/notification_service_spec.rb

@@ -233,15 +233,15 @@ describe NotificationService do
         should_email(@u_watcher.id)
         should_not_email(@u_participating.id)
         should_not_email(@u_disabled.id)
-        notification.merge_mr(merge_request)
+        notification.merge_mr(merge_request, @u_disabled)
       end
       def should_email(user_id)
-        Notify.should_receive(:merged_merge_request_email).with(user_id, merge_request.id)
+        Notify.should_receive(:merged_merge_request_email).with(user_id, merge_request.id, @u_disabled.id)
       end
       def should_not_email(user_id)
-        Notify.should_not_receive(:merged_merge_request_email).with(user_id, merge_request.id)
+        Notify.should_not_receive(:merged_merge_request_email).with(user_id, merge_request.id, @u_disabled.id)
       end
     end
   end