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())
``list_volumes`` returns a ``BlockVolume`` for each unattached volume
dataset/ETHPy150Open ClusterHQ/flocker/flocker/node/agents/test/test_blockdevice.py/LoopbackBlockDeviceAPIImplementationTests.test_list_unattached_volumes