code: def test___prepare_bigdl_env(self):
      # BigDL will automatically execute 'prepare_env()' function which
      # includes '__prepare_bigdl_env()'. To test if there's no more duplicate
      #  adding jar path message, just do prepare_env()' again
      # to see if the log is correct and the environment variables should not vary.
  
      from bigdl.dllib.utils.engine import prepare_env
  
      bigdl_jars_env_1 = os.environ.get("BIGDL_JARS", None)
      spark_class_path_1 = os.environ.get("SPARK_CLASSPATH", None)
      sys_path_1 = sys.path
      prepare_env()
      # there should be no duplicate messages about adding jar path to
      # the environment var "BIGDL_JARS"
      # environment variables should remain the same
      bigdl_jars_env_2 = os.environ.get("BIGDL_JARS", None)
      spark_class_path_2 = os.environ.get("SPARK_CLASSPATH", None)
      sys_path_2 = sys.path
      assert bigdl_jars_env_1 == bigdl_jars_env_2
      assert spark_class_path_1 == spark_class_path_2
      assert sys_path_1 == sys_path_2
  
imports: import pytest
  import os
  from bigdl.dllib.utils.common import *
label_desc: Use image node_id 3 for calling the TestEngineEnv obj's underlying member method code with example usage: obj.test___prepare_bigdl_env() without return types