code: def on_test_start(self) -> None:
      self._starting_epoch = self.trainer.current_epoch
      self._in_testing_loop = True
  
      for t in self._trainers:
          t.on_test_start()
  
imports: import bisect
  import functools
  import itertools
  from collections import OrderedDict
  from typing import Dict, List, Tuple
  import torch.nn
  from pytorch_lightning.loops.optimization.optimizer_loop import ClosureResult
  from reagent.core.utils import lazy_property
  from .reagent_lightning_module import ReAgentLightningModule
label_desc: Use image node_id 8 for calling the MultiStageTrainer obj's underlying member method code with example usage: obj.on_test_start() without return types