code: def test_symb_block_import_backward_compatible(block_type) -> None:
      x1 = mx.nd.array([1, 2, 3])
      x2 = [mx.nd.array([1, 5, 5]), mx.nd.array([2, 3, 3])]
  
      my_block = block_type()
      my_block.collect_params().initialize()
      my_block.hybridize()
      my_block(x1, x2)
  
      with tempfile.TemporaryDirectory(
          prefix="gluonts-estimator-temp-"
      ) as temp_dir:
          temp_path = Path(temp_dir)
  
          export_symb_block(my_block, temp_path, "gluonts-model")
  
          format_json_path = (
              temp_path / "gluonts-model-in_out_format.json"
          )
  
          assert format_json_path.exists()
          try:
              format_json_path.unlink()
              import_symb_block(3, temp_path, "gluonts-model")
          except FileNotFoundError:
              pytest.fail(
                  "Symbol block import fails when format json is not in path"
              )
  
file_path: gluonts/test/mx/test_mx_util.py
imports: import pytest
  import itertools
  import tempfile
  from pathlib import Path
  from typing import List
  import mxnet
  import numpy
  from gluonts.mx import Tensor
  from gluonts.mx.util import cumsum, export_symb_block, hybrid_block_to_symbol_block, import_symb_block, mx_switch, weighted_average
label_desc: Use image node_id 4 for calling a global function with example usage: test_symb_block_import_backward_compatible(block_type) without return types