code: def test_unknown_font(caplog):
      with caplog.at_level("WARNING"):
          mpl.rcParams["font.family"] = "this-font-does-not-exist"
          plt.figtext(0.5, 0.5, "hello, world")
          plt.savefig(BytesIO(), format="pgf")
      assert "Ignoring unknown font: this-font-does-not-exist" in [
          r.getMessage() for r in caplog.records
      ]
  
imports: import datetime
  from io import BytesIO
  import os
  import shutil
  import numpy
  from packaging.version import parse
  import pytest
  import matplotlib
  import matplotlib.pyplot
  from matplotlib.testing import _has_tex_package, _check_for_pgf
  from matplotlib.testing.exceptions import ImageComparisonFailure
  from matplotlib.testing.compare import compare_images
  from matplotlib.backends.backend_pgf import PdfPages
  from matplotlib.testing.decorators import _image_directories, check_figures_equal, image_comparison
  from matplotlib.testing._markers import needs_ghostscript, needs_pgf_lualatex, needs_pgf_pdflatex, needs_pgf_xelatex
label_desc: Use image node_id 16 for calling a global function with example usage: test_unknown_font(caplog) without return types