human
Here's a good function header given the following:
I wrote the below code

    pool = fixture(test)
    service = service_for_pool(test, pool)
    volume = service.get(MY_VOLUME)
    pool2 = fixture(test)
    service2 = service_for_pool(test, pool2)
    volume2 = Volume(node_id=service.node_id, name=MY_VOLUME, service=service2)
    d = pool.create(volume)
    def created_filesystem(filesystem):
        path = filesystem.get_path()
        path.child('file').setContent('some    bytes')
        path.child('directory').makedirs()
        copying = copy(volume, volume2)
        copying.addCallback((lambda ignored: CopyVolumes(from_volume=volume, to_volume=volume2)))
        return copying
    d.addCallback(created_filesystem)
    return d

What's a good function header?
assistant
#Here's a good function header.

def create_and_copy(test, fixture):