Steps to reproduce:

1. Visit https://www.zabbix.com/documentation/5.0/en/manual/config/notifications/media#media-type-testing

Result:
It is logical and relevant that media types should be tested directly by Zabbix server (also when initiated from Zabbix frontend), but I don't see it explicitly specified in this documentation.
Expected:
I believe, there could be explicitly explained, which Zabbix component is performing the test in the background.