code: def test_num_envs(self):
      self.assertEqual(self.vec_env.num_envs, self.num_envs)
  
file_path: chainerrl/tests/envs_tests/test_vector_envs.py
imports: import unittest
  from chainer import testing
  import gym
  import numpy
  import chainerrl
label_desc: Use image node_id 3 for calling the TestSerialVectorEnv obj's underlying member method code with example usage: obj.test_num_envs() without return types