code: def __prepare_fancyarrow_dpi_cor_test():
      """
      Convenience function that prepares and returns a FancyArrowPatch. It aims
      at being used to test that the size of the arrow head does not depend on
      the DPI value of the exported picture.
  
      NB: this function *is not* a test in itself!
      """
      fig2 = plt.figure(
          "fancyarrow_dpi_cor_test", figsize=(4, 3), dpi=50
      )
      ax = fig2.add_subplot()
      ax.set_xlim([0, 1])
      ax.set_ylim([0, 1])
      ax.add_patch(
          mpatches.FancyArrowPatch(
              posA=(0.3, 0.4),
              posB=(0.8, 0.6),
              lw=3,
              arrowstyle="->",
              mutation_scale=100,
          )
      )
      return fig2
  
file_path: matplotlib/lib/matplotlib/tests/test_arrow_patches.py
imports: import pytest
  import platform
  import matplotlib.pyplot
  from matplotlib.testing.decorators import image_comparison
  import matplotlib.patches
label_desc: Use image node_id 4 for calling a global function with example usage: __prepare_fancyarrow_dpi_cor_test() and returns: fig2