code: def test_pdf_append_to_bytesio():
      im = hopper("RGB")
      f = io.BytesIO()
      im.save(f, format="PDF")
      initial_size = len(f.getvalue())
      assert initial_size > 0
      im = hopper("P")
      f = io.BytesIO(f.getvalue())
      im.save(f, format="PDF", append=True)
      assert len(f.getvalue()) > initial_size
  
imports: from __future__ import annotations
  import io
  import os
  import os.path
  import tempfile
  import time
  import pytest
  from PIL import Image, PdfParser, features
  from .helper import hopper, mark_if_feature_version, skip_unless_feature
label_desc: Use image node_id 16 for calling a global function with example usage: test_pdf_append_to_bytesio() without return types