Comment 1 for bug 1816538

AFAICT this isn't an issue with swap_volume itself. The fixture is causing the TypeError on purpose here to exercise the notification code path when dealing with errors during a swap volume call:

https://github.com/openstack/nova/blob/d2a87a44468f91d5a468e1262e7e2fd8c7add35c/nova/tests/functional/notification_sample_tests/test_instance.py#L1564-L1565

https://github.com/openstack/nova/blob/d2a87a44468f91d5a468e1262e7e2fd8c7add35c/nova/tests/fixtures.py#L1597-L1601

You missed the trace showing the issue with the notification path itself from your initial comment:

Traceback (most recent call last):
  File "/home/zuul/src/git.openstack.org/openstack/nova/nova/tests/functional/notification_sample_tests/test_instance.py", line 1609, in test_volume_swap_server_with_error
    tb2 = fake_notifier.VERSIONED_NOTIFICATIONS[7]['payload'][
IndexError: list index out of range