code: def test_png_transparency():  # Actually, also just testing that png works.
      buf = BytesIO()
      plt.figure().savefig(
          buf, format="png", backend="pgf", transparent=True
      )
      buf.seek(0)
      t = plt.imread(buf)
      assert (t[..., 3] == 0).all()
  
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 15 for calling a global function with example usage: test_png_transparency() without return types