posthog-js supports person.set_once but our backend doesn't. Make sure we can pass through `$set_once` on an `$identify` call, and only set the properties within if the properties aren't already set on the user.
posthog/tasks/test/test_process_event.py
process_event(
                "xxx",
                "",
                "",
                {"event": ["event name", "a list"], "properties": {"price": 299.99, "name": "AirPods Pro"},},
                self.team.pk,
                now().isoformat(),
                now().isoformat(),
            )
            event = get_events()[0]
            self.assertEqual(event.event, '["event name", "a list"]')
        def test_long_event_name_substr(self) -> None:
            process_event(
                "xxx",
                "",
                "",
                {"event": "E" * 300, "properties": {"price": 299.99, "name": "AirPods Pro"},},
                self.team.pk,
                now().isoformat(),
                now().isoformat(),
            )
            event = get_events()[0]
            self.assertEqual(len(event.event), 200)
    return TestProcessEvent
class TestProcessEvent(test_process_event_factory(_process_event, Event.objects.all, SessionRecordingEvent.objects.all, get_elements)):  # type: ignore
    pass