code: def test_should_be_serializable_into_dir_when_empty(self):
      # Given
      nlu_engine = SnipsNLUEngine()
  
      # When
      nlu_engine.persist(self.tmp_file_path)
  
      # Then
      expected_dict = {
          "unit_name": "nlu_engine",
          "dataset_metadata": None,
          "config": None,
          "intent_parsers": [],
          "builtin_entity_parser": None,
          "custom_entity_parser": None,
          "model_version": snips_nlu.__model_version__,
          "training_package_version": snips_nlu.__version__,
      }
      self.assertJsonContent(
          self.tmp_file_path / "nlu_engine.json", expected_dict
      )
  
imports: from __future__ import unicode_literals
  import io
  import shutil
  import sys
  from builtins import str
  from unittest import skipIf
  from checksumdir import dirhash
  from mock import MagicMock, patch
  from snips_nlu_parsers import get_all_languages
  import snips_nlu
  from snips_nlu.common.io_utils import temp_dir
  from snips_nlu.constants import END, LANGUAGE, LANGUAGE_EN, RES_ENTITY, RES_INPUT, RES_INTENT, RES_INTENT_NAME, RES_MATCH_RANGE, RES_RAW_VALUE, RES_SLOTS, RES_SLOT_NAME, RES_VALUE, START
  from snips_nlu.dataset import Dataset, validate_and_format_dataset
  from snips_nlu.entity_parser import BuiltinEntityParser, CustomEntityParser, CustomEntityParserUsage
  from snips_nlu.exceptions import IntentNotFoundError, InvalidInputError, NotTrained, IncompatibleModelError, PersistingError, LoadingError
  from snips_nlu.intent_parser import IntentParser
  from snips_nlu.nlu_engine import SnipsNLUEngine
  from snips_nlu.pipeline.configs import NLUEngineConfig
  from snips_nlu.resources import load_resources
  from snips_nlu.result import custom_slot, empty_result, intent_classification_result, parsing_result, resolved_slot, unresolved_slot, extraction_result
  from snips_nlu.tests.utils import FixtureTest, MockIntentParser, get_empty_dataset
label_desc: Use image node_id 13 for calling the TestSnipsNLUEngine obj's underlying member method code with example usage: obj.test_should_be_serializable_into_dir_when_empty() without return types