docstr: Tests that metadata content must be passed as a serialized
  string.
code: def test_metadata_format(self):
      """Tests that metadata content must be passed as a serialized
      string."""
      with self.assertRaisesRegex(
          TypeError, r"Content type must be bytes."
      ):
          metadata.parse_plugin_metadata(123)
  
file_path: tensorboard/tensorboard/plugins/mesh/metadata_test.py
imports: import tensorflow
  from tensorboard.plugins.mesh import metadata
  from tensorboard.plugins.mesh import plugin_data_pb2
label_desc: Use image node_id 6 for calling the MetadataTest obj's underlying member method code with example usage: obj.test_metadata_format() without return types