Mocking ConfigObj instances

Using ConfigObj, I want to test some section creation code:

def create_section(config, section):
    config.reload()
    if section not in config:
         config[session] = {}
         logging.info("Created new section %s.", section)
    else:
         logging.debug("Section %s already exists.", section)

I would like to write a few unit tests but I am hitting a problem. For example,

def test_create_section_created():
    config = Mock(spec=ConfigObj)  # ← This is not right…
    create_section(config, 'ook')
    assert 'ook' in config
    config.reload.assert_called_once_with()

Clearly, the test method will fail because of a TypeError as the argument of type 'Mock' is not iterable.

How can I define the config object as a mock?