code: def test_save_freq_unknown_error(self):
      with self.assertRaisesRegex(
          ValueError, expected_regex="Invalid value"
      ):
          callbacks.BackupAndRestore(
              backup_dir="backup_dir", save_freq="batch"
          )
  
      with self.assertRaisesRegex(
          ValueError, expected_regex="Invalid value"
      ):
          callbacks.BackupAndRestore(
              backup_dir="backup_dir", save_freq=0.15
          )
  
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 2 for calling the BackupAndRestoreCallbackTest obj's underlying member method code with example usage: obj.test_save_freq_unknown_error() without return types