':param dict units: A dictionary of canned ``Unit``\ s which will be
manipulated and returned by the methods of this
``FakeDockerClient``.
:type units: ``dict`` mapping `unit_name` to ``Unit``\ .'

def __init__(self, units=None):

    if (units is None):
        units = {}
    self._units = units
    self._used_ports = pset()
