Initial work to add notification reason to emails

Adds `#build_notification_recipients` to `NotificationRecipientService`
that returns the `NotificationRecipient` objects in order to be able to
access the new attribute `reason`.

This new attribute is used in the different notifier methods in order to
add the reason as a header: `X-GitLab-NotificationReason`.

Only the reason with the most priority gets sent.

1 files changed, 4 insertions, 2 deletions

diff --git a/spec/workers/new_merge_request_worker_spec.rb b/spec/workers/new_merge_request_worker_spec.rb
index 9e0cbde45b1..c3f29a40d58 100644
--- a/spec/workers/new_merge_request_worker_spec.rb
+++ b/spec/workers/new_merge_request_worker_spec.rb
@@ -46,8 +46,10 @@ describe NewMergeRequestWorker do
         expect { worker.perform(merge_request.id, user.id) }.to change { Event.count }.from(0).to(1)
       end
 
-      it 'creates a notification for the assignee' do
-        expect(Notify).to receive(:new_merge_request_email).with(mentioned.id, merge_request.id).and_return(double(deliver_later: true))
+      it 'creates a notification for the mentioned user' do
+        expect(Notify).to receive(:new_merge_request_email)
+                            .with(mentioned.id, merge_request.id, NotificationReason::MENTIONED)
+                            .and_return(double(deliver_later: true))
 
         worker.perform(merge_request.id, user.id)
       end