code: def test_backup_dir_empty_error(self):
      with self.assertRaisesRegex(
          ValueError,
          expected_regex="Empty `backup_dir` argument passed",
      ):
          callbacks.BackupAndRestore(backup_dir="", save_freq="epoch")
  
imports: import numpy
  import pytest
  from keras import callbacks
  from keras import layers
  from keras import testing
  from keras.models import Sequential
  from keras.utils import file_utils
label_desc: Use image node_id 6 for calling the BackupAndRestoreCallbackTest obj's underlying member method code with example usage: obj.test_backup_dir_empty_error() without return types