code: def test_save_buffer(self):
      im = pyvips.Image.black(10, 20)
      buf = im.write_to_buffer(".jpg")
      assert len(buf) > 100
  
file_path: pyvips/tests/test_saveload.py
imports: import os
  import tempfile
  import pytest
  import pyvips
  from helpers import temp_filename, skip_if_no, _is_PY3, IMAGES, JPEG_FILE
label_desc: Use image node_id 6 for calling the TestSaveLoad obj's underlying member method code with example usage: obj.test_save_buffer() without return types