code: def test_actor_backface_prop(actor):
      actor.prop.opacity = 0.5
      assert isinstance(actor.backface_prop, pv.Property)
      assert actor.backface_prop.opacity == actor.prop.opacity
      actor.backface_prop.opacity = 1.0
      assert actor.backface_prop.opacity == 1.0
  
      actor.backface_prop = None
      assert actor.backface_prop.opacity == actor.prop.opacity
  
imports: import platform
  import numpy
  import pytest
  import vtk
  import pyvista
  from pyvista import examples
label_desc: Use image node_id 21 for calling a global function with example usage: test_actor_backface_prop(actor) without return types