code: def test_block_untrusted(self):
      # block all untrusted operations
      pyvips.block_untrusted_set(True)
  
      # should fail
      with pytest.raises(Exception):
          _ = pyvips.Image.new_from_file(SVG_FILE)
  
      # reenable all loads
      pyvips.block_untrusted_set(False)
  
imports: import tempfile
  import pytest
  import pyvips
  from helpers import skip_if_no, JPEG_FILE, WEBP_FILE, SVG_FILE
label_desc: Use image node_id 3 for calling the TestBlock obj's underlying member method code with example usage: obj.test_block_untrusted() without return types