code: def test_normalize_observation():
      env = DummyRewardEnv(return_reward_idx=0)
      env = NormalizeObservation(env)
      env.reset()
      env.step(env.action_space.sample())
      assert_almost_equal(env.obs_rms.mean, 0.5, decimal=4)
      env.step(env.action_space.sample())
      assert_almost_equal(env.obs_rms.mean, 1.0, decimal=4)
  
file_path: gym/tests/wrappers/test_normalize.py
imports: from typing import Optional
  import numpy
  from numpy.testing import assert_almost_equal
  import gym
  from gym.wrappers.normalize import NormalizeObservation, NormalizeReward
label_desc: Use image node_id 2 for calling a global function with example usage: test_normalize_observation() without return types