async def METHOD_NAME(self):
    r1 = Router()
    r2 = Router()
    r3 = Router()
    r3.observers["custom-event"] = TelegramEventObserver(r3, event_name="custom-event")
    async def handler(evt):
        return evt
    r1.include_router(r2)
    r1.include_router(r3)
    r3.observers["custom-event"].register(handler)
    assert await r1.propagate_event(update_type="custom-event", event=None) is None
    assert await r2.propagate_event(update_type="custom-event", event=None) is UNHANDLED
    assert await r3.propagate_event(update_type="custom-event", event=None) is None