class_docstr: A generic testing environment for use in testing with modified environments are required.
class_docstr_tok: ["A","generic","testing","environment","for","use","in","testing","with","modified","environments","are","required","."]
code: def step(self, action: ActType) -> Tuple[ObsType, float, bool, dict]:
      raise NotImplementedError("TestingEnv step_fn is not set.")
  
file_path: gym/tests/testing_env.py
imports: import types
  from typing import Any, Dict, Optional, Tuple, Union
  import gym
  from gym import spaces
  from gym.core import ActType, ObsType
  from gym.envs.registration import EnvSpec
label_desc: Use image node_id 3 for calling the GenericTestEnv obj's underlying member method code with example usage: obj.step(action) without return types