code: def train(self):
      ExperimentRunnerTest._trainer_calls += 1
      if self.trained:
          raise ValueError()
      self.trained = True
  
imports: import io
  import json
  import logging
  import shutil
  import tempfile
  from pathlib import Path
  from typing import Dict, Any
  from unittest import TestCase
  import toml
  from transfer_nlp.plugins.config import register_plugin, ExperimentConfig
  from transfer_nlp.plugins.reporters import ReporterABC
  from transfer_nlp.plugins.trainer_abc import TrainerABC
  from transfer_nlp.runner.experiment_runner import ExperimentRunner
label_desc: Use image node_id 2 for calling the MockTrainer obj's underlying member method code with example usage: obj.train() without return types