code: def test_graph_def(self, backend):
      with tf.Graph().as_default() as graph:
          x = tf.placeholder(tf.float32, shape=(3, 4, 5))
          out = tf.nn.relu(x)
          mlmodel = converter.convert(
              graph,
              inputs=[TensorType(x.op.name, (3, 4, 5))],
              outputs=[out.op.name],
              convert_to=backend[0],
          )
          assert mlmodel is not None
  
imports: import os
  import shutil
  import tempfile
  import numpy
  import pytest
  import coremltools
  import coremltools.converters
  import coremltools.proto.FeatureTypes_pb2
  from coremltools import EnumeratedShapes, ImageType, RangeDim, TensorType
  from coremltools._deps import _HAS_TF_1, _IS_MACOS, MSG_TF1_NOT_FOUND
  from coremltools.converters.mil.frontend.tensorflow.converter import TFConverter
  from coremltools.converters.mil.frontend.tensorflow.test.testing_utils import TensorFlowBaseTest, get_tf_keras_io_names, make_tf_graph
  from coremltools.converters.mil.testing_reqs import backends
  from coremltools.converters.mil.testing_utils import random_gen
label_desc: Use image node_id 3 for calling the TestTf1ModelFormats obj's underlying member method code with example usage: obj.test_graph_def(backend) without return types