'Test diff restore not allowed when backup not diff-format.'

@common_mocks
def test_diff_restore_allowed_with_image_not_exists(self):

    not_allowed = (False, None)
    backup_base = 'backup.base'
    rbd_io = self._get_wrapped_rbd_io(self.service.rbd.Image())
    args_vols_different = [backup_base, self.backup, self.alt_volume, rbd_io, self.mock_rados]
    with mock.patch.object(self.service, '_rbd_image_exists') as mock_rbd_image_exists:
        mock_rbd_image_exists.return_value = (False, backup_base)
        resp = self.service._diff_restore_allowed(*args_vols_different)
        self.assertEqual(not_allowed, resp)
        mock_rbd_image_exists.assert_called_once_with(backup_base, self.backup['volume_id'], self.mock_rados)
