code: def validate(self):
      assert len(self.finished) == self.length
      for k, v in self.counter.items():
          assert v == k * 3 % 5 + 1
  
imports: from collections import Counter
  import gym
  import numpy
  from tianshou.data import Batch, Collector
  from tianshou.policy import BasePolicy
  from torch.utils.data import DataLoader, Dataset, DistributedSampler
  from qlib.rl.utils.finite_env import LogWriter, FiniteDummyVectorEnv, FiniteShmemVectorEnv, FiniteSubprocVectorEnv, check_nan_observation, generate_nan_observation
label_desc: Use image node_id 3 for calling the MetricTracker obj's underlying member method code with example usage: obj.validate() without return types