'``list_volumes`` returns a ``BlockVolume`` for each unattached volume
file.'

def test_list_unattached_volumes(self):

    expected_size = self.minimum_allocatable_size
    expected_dataset_id = uuid4()
    blockdevice_volume = _blockdevicevolume_from_dataset_id(size=expected_size, dataset_id=expected_dataset_id)
    with self.api._root_path.child('unattached').child(_backing_file_name(blockdevice_volume)).open('wb') as f:
        f.truncate(expected_size)
    self.assertEqual([blockdevice_volume], self.api.list_volumes())
