code: def test_concrete_function_list_from_tf_low_level_api(self):
      root = tf.train.Checkpoint()
      root.v1 = tf.Variable(3.0)
      root.v2 = tf.Variable(2.0)
      root.f = tf.function(lambda x: root.v1 * root.v2 * x)
  
      input_data = tf.constant(1.0, shape=[1, 1])
      to_save = root.f.get_concrete_function(input_data)
      tf.saved_model.save(root, self.saved_model_dir, to_save)
  
      tf_model = tf.saved_model.load(self.saved_model_dir)
      concrete_func = tf_model.signatures[
          tf.saved_model.DEFAULT_SERVING_SIGNATURE_DEF_KEY
      ]
      mlmodel = converter.convert(
          [concrete_func], outputs="Identity", source=frontend
      )
      assert mlmodel is not None
  
imports: import os
  import shutil
  import tempfile
  import pytest
  import coremltools.converters
  from coremltools.converters.mil.input_types import TensorType
  from coremltools.converters.mil.frontend.tensorflow.test.testing_utils import get_tf_keras_io_names
  from coremltools.converters.mil.frontend.tensorflow.test import testing_utils
  from coremltools.converters.mil.frontend.tensorflow2.test.testing_utils import make_tf2_graph, run_compare_tf2
  from coremltools.converters.mil.frontend.tensorflow.test.test_load import frontend, TestTf1ModelInputsOutputs
label_desc: Use image node_id 6 for calling the TestTf2ModelFormats obj's underlying member method code with example usage: obj.test_concrete_function_list_from_tf_low_level_api() without return types