code: def test_default_filename(self):
      plots = list(p())
      save_as_pdf_pages(plots, verbose=False)
      fn = plots[0]._save_filename("pdf")
      assert_exist_and_clean(fn, "default filename")
  
file_path: plotnine/tests/test_save_as_pdf_pages.py
imports: import warnings
  from pathlib import Path
  import matplotlib.pyplot
  import pytest
  from plotnine import aes, geom_text, ggplot, ggtitle, theme
  from plotnine.data import mtcars
  from plotnine.exceptions import PlotnineError, PlotnineWarning
  from plotnine.ggplot import save_as_pdf_pages
label_desc: Use image node_id 1 for calling the TestArguments obj's underlying member method code with example usage: obj.test_default_filename() without return types