I\'m admin of my test app, and my test page.
Now I\'m doing a function get page\'s feed realtime by webhook, just only on development mode.
When I click test but
It is not possible to run this service without an app review, since it is not possible to add the 'mange_pages' permission to a (test-)user within a development app. At the same time it is not possible to turn a testapp into live-mode. As the same is true vice versa the only solution is the app review to get information from a specific (test-)page.
For live testing i suggest to create a testuser and subscribe for information about the "user" to test your webhook.
You can check with GET graph.facebook.com/app-id/subscriptions
, if your app is successfully subscribed to "page information". Graph API Documentation
As you already mentioned you can also send "page information" test calls to your endpoint.
UPDATE 18th Nov 2018
If you go to Webhook -> pages in your App Dashboard on https://developers.facebook.com you are able to notice, that Webhooks in dev mode do not work.