code: def test_None_zorder():
      fig, ax = plt.subplots()
      (ln,) = ax.plot(range(5), zorder=None)
      assert ln.get_zorder() == mlines.Line2D.zorder
      ln.set_zorder(123456)
      assert ln.get_zorder() == 123456
      ln.set_zorder(None)
      assert ln.get_zorder() == mlines.Line2D.zorder
  
imports: import io
  from itertools import chain
  import numpy
  import pytest
  import matplotlib.colors
  import matplotlib.pyplot
  import matplotlib.patches
  import matplotlib.lines
  import matplotlib.path
  import matplotlib.transforms
  import matplotlib.collections
  import matplotlib.artist
  import matplotlib.backend_bases
  import matplotlib
  from matplotlib.testing.decorators import check_figures_equal, image_comparison
label_desc: Use image node_id 11 for calling a global function with example usage: test_None_zorder() without return types