ckeditor_mentions-8.x-2.x-dev/tests/modules/ckeditor_mentions_events_test/ckeditor_mentions_user_events.services.yml

services:
  ckeditor_mentions_events_test.mention_event_subscriber:
    class: Drupal\ckeditor_mentions_events_test\EventSubscriber\CkeditorMentionsSuggestionTestSubscriber
    tags:
      - { name: 'event_subscriber' }