How to test the "preview" web hook

As the developer of an app, how can I test webhooks like “preview”, “new-install”, etc? How can I verify what data would be provided in the webhook if I were to publish my app? I can provoke “option-change” events and “item-add” events from the developer dashboard, but that’s about all.
Generally, how can I verify that the app will work for someone that is not the developer of the app, without actually publishing the app?

Thank you.

I’ll explain why I’m asking.
My app does not require a service account, however I would like to know who is using the app so I can contact them. When I view the app in the developer console, the “user”.“email” field is always blank. When I install my app on my own site, I can generate a “new-install” event, but again the “user”.“email” field is blank, even though I’m asked to provide consent for sharing my email address with the developer.
Is this field blank because I am testing my own, unpublished app, or will it also be blank when other customers install my published app?