While debugging a failure in a downstream patch, I noticed a unit test was failing due to a missing config registration:

==============================
Failed 1 tests - output below:
==============================

networking_ovn.tests.unit.agent.metadata.test_driver.TestMetadataDriverProcess.test_spawn_metadata_proxy
--------------------------------------------------------------------------------------------------------

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    b'Traceback (most recent call last):'
    b'  File "/networking-ovn/.tox/py36/lib/python3.6/site-packages/oslo_config/cfg.py", line 2193, in __getattr__'
    b'    return self._get(name)'
    b'  File "/networking-ovn/.tox/py36/lib/python3.6/site-packages/oslo_config/cfg.py", line 2627, in _get'
    b'    value, loc = self._do_get(name, group, namespace)'
    b'  File "/networking-ovn/.tox/py36/lib/python3.6/site-packages/oslo_config/cfg.py", line 2645, in _do_get'
    b'    info = self._get_opt_info(name, group)'
    b'  File "/networking-ovn/.tox/py36/lib/python3.6/site-packages/oslo_config/cfg.py", line 2845, in _get_opt_info'
    b'    raise NoSuchOptError(opt_name, group)'
    b'oslo_config.cfg.NoSuchOptError: no such option enable_rate_limiting in group [DEFAULT]'
    b''
    b'During handling of the above exception, another exception occurred:'
    b''
    b'Traceback (most recent call last):'
    b'  File "/networking-ovn/.tox/py36/lib/python3.6/site-packages/neutron/tests/base.py", line 181, in func'
    b'    return f(self, *args, **kwargs)'
    b'  File "/networking-ovn/networking_ovn/tests/unit/agent/metadata/test_driver.py", line 80, in test_spawn_metadata_proxy'
    b'    network_id=datapath_id)'
    b'  File "/networking-ovn/networking_ovn/agent/metadata/driver.py", line 237, in spawn_monitored_metadata_proxy'
    b'    pm.enable()'
    b'  File "/networking-ovn/.tox/py36/lib/python3.6/site-packages/neutron/agent/linux/external_process.py", line 86, in enable'
    b'    cmd = cmd_callback(self.get_pid_file_name())'
    b'  File "/networking-ovn/networking_ovn/agent/metadata/driver.py", line 219, in callback'
    b'    haproxy.create_config_file()'
    b'  File "/networking-ovn/networking_ovn/agent/metadata/driver.py", line 159, in create_config_file'
    b'    if cfg.CONF.enable_rate_limiting:'
    b'  File "/networking-ovn/.tox/py36/lib/python3.6/site-packages/oslo_config/cfg.py", line 2197, in __getattr__'
    b'    raise NoSuchOptError(name)'
    b'oslo_config.cfg.NoSuchOptError: no such option enable_rate_limiting in group [DEFAULT]'

This option was added to the code in commit 361928d16e9006d9d438e9663c3101bd59d1b785, https://code.engineering.redhat.com/gerrit/c/networking-ovn/+/239104 (Rate limit of metadata requests).

The problem is the unit test never called to register this new option as is done in other tests.

I also noticed the driver code itself doesn't register the options, although it does seem to work.