Sends a test delivery to the registration's URL immediately and answers with what happened. The response is 200 rather than 202, because the attempt has already been made.
Signature and delivery history
The test is a real delivery in every respect but its type. It carries the webhook.test event type and is signed under the registration's own scheme with the same headers as any delivery, so verification proven against it holds for real events. It appears in delivery history, can be read by id, and can be replayed.
Retries and suspension
A failed test is not discarded. It joins the ordinary retry ladder and counts toward endpoint suspension.
Registration status
An INACTIVE registration returns 409 Conflict. SUSPENDED is allowed, and a successful test resets the consecutive-failure count.
Automatic test delivery
A test delivery is also queued automatically when a registration is created.

