Send Calendar Event Message Test

Builds the event's message from its settings exactly as Create Message would and sends it immediately as a test message (is_test) to emails, or to numbers for SMS events, the same as a Create Message test. The event's own message and approval rounds are not changed, and the test appears with other test messages. Allowed only while the event could be sent for approval: it must be ready (or denied or cancelled with nothing missing), and not have a message waiting for approval, approved, or sent. Returns the created test message.