code: def test_human_readable_custom():
      """Test human_readable formatter option"""
      f = formatters.HumanReadable()
      assert f(None) == "∅"
      f = formatters.HumanReadable(none_char="/")
      assert f(None) == "/"
  
label_desc: Use image node_id 2 for calling a global function with example usage: test_human_readable_custom() without return types