docstr: convert mlmodel to spec, and then back to mlmodel and verify that it works
docstr_tok: ["convert","mlmodel","to","spec",",","and","then","back","to","mlmodel","and","verify","that","it","works"]
code: def test_mlmodel_to_spec_to_mlmodel_with_no_weights_model(self):
      """
      convert mlmodel to spec, and then back to mlmodel and verify that it works
      """
      spec = self.mlmodel_no_weights.get_spec()
      # if no weights_dir is passed, error will be raised
      with pytest.raises(
          Exception,
          match="MLModel of type mlProgram cannot be loaded just from the model "
          "spec object. It also needs the path to the weights file. "
          "Please provide that as well, using the 'weights_dir' argument.",
      ):
          MLModel(spec)
  
      # weights_dir will still exist, even though the model has no weights,
      # with a weights file that only has header and no data
      weights_dir = self.mlmodel_no_weights.weights_dir
      assert weights_dir is not None
      mlmodel_from_spec = MLModel(spec, weights_dir=weights_dir)
      self._test_mlmodel_correctness(mlmodel_from_spec)
  
      # load mlmodel from spec using an empty weights_dir
      with tempfile.TemporaryDirectory() as empty_weight_dir:
          mlmodel_from_spec = MLModel(spec, weights_dir=weights_dir)
          self._test_mlmodel_correctness(mlmodel_from_spec)
  
imports: import os
  import shutil
  import tempfile
  import numpy
  import pytest
  import coremltools
  from coremltools import ComputeUnit, utils
  from coremltools._deps import _HAS_TORCH
  from coremltools.converters.mil import Builder
  from coremltools.libmodelpackage import ModelPackage
  from coremltools.models import MLModel
  from coremltools.models.utils import _MLPACKAGE_AUTHOR_NAME, _WEIGHTS_DIR_NAME
  from coremltools.proto import Model_pb2
label_desc: Use image node_id 10 for calling the TestSpecAndMLModelAPIs obj's underlying member method code with example usage: obj.test_mlmodel_to_spec_to_mlmodel_with_no_weights_model() without return types