code: def test_get_text_instances(self):
      with self.assertRaises(NotImplementedError):
          BaseTextDetPostProcessor().get_text_instances(None, None)
  
file_path: mmocr/tests/test_models/test_textdet/test_postprocessors/test_base_postprocessor.py
imports: import unittest
  from unittest import mock
  import numpy
  import torch
  from mmengine.structures import InstanceData
  from mmocr.models.textdet.postprocessors import BaseTextDetPostProcessor
  from mmocr.structures import TextDetDataSample
label_desc: Use image node_id 4 for calling the TestBaseTextDetPostProcessor obj's underlying member method code with example usage: obj.test_get_text_instances() without return types