class_docstr: Callback that measures the training and testing time of a PyTorch Lightning module.
docstr: Call when the test begins.
  
  Sets the start time to the time testing started.
  Goes over all the test dataloaders and adds the number of images in each.
  
  Args:
      trainer (Trainer): PyTorch Lightning trainer.
      pl_module (LightningModule): Current training module.
  
  Returns:
      None
code: def on_test_start(
      self, trainer: Trainer, pl_module: LightningModule
  ) -> None:  # pylint: disable=W0613
      """Call when the test begins.
  
      Sets the start time to the time testing started.
      Goes over all the test dataloaders and adds the number of images in each.
  
      Args:
          trainer (Trainer): PyTorch Lightning trainer.
          pl_module (LightningModule): Current training module.
  
      Returns:
          None
      """
      self.start = time.time()
      self.num_images = 0
  
      if trainer.test_dataloaders is not None:  # Check to placate Mypy.
          for dataloader in trainer.test_dataloaders:
              self.num_images += len(dataloader.dataset)
  
file_path: anomalib/src/anomalib/utils/callbacks/timer.py
imports: import logging
  import time
  from pytorch_lightning import Callback, LightningModule, Trainer
label_desc: Use image node_id 4 for calling the TimerCallback obj's underlying member method code with example usage: obj.on_test_start(trainer, pl_module) without return types