code: def test_register_extensions(self):
      test_format = "a"
      exts = ["b", "c"]
      for ext in exts:
          Image.register_extension(test_format, ext)
      ext_individual = Image.EXTENSION.copy()
      for ext in exts:
          del Image.EXTENSION[ext]
  
      Image.register_extensions(test_format, exts)
      ext_multiple = Image.EXTENSION.copy()
      for ext in exts:
          del Image.EXTENSION[ext]
  
      assert ext_individual == ext_multiple
  
imports: import io
  import os
  import shutil
  import sys
  import tempfile
  import pytest
  from PIL import Image, ImageDraw, ImagePalette, UnidentifiedImageError
  from .helper import assert_image_equal, assert_image_equal_tofile, assert_image_similar_tofile, assert_not_all_same, hopper, is_win32, mark_if_feature_version, skip_unless_feature
label_desc: Use image node_id 41 for calling the TestImage obj's underlying member method code with example usage: obj.test_register_extensions() without return types