code: def test_ddp_with_2_gpus():
      """Tests if device is set correctly when training and after teardown for DDPStrategy."""
      trainer = Trainer(
          accelerator="gpu",
          devices=2,
          strategy="ddp",
          fast_dev_run=True,
          enable_progress_bar=False,
          enable_model_summary=False,
      )
      # assert strategy attributes for device setting
      assert isinstance(trainer.strategy, DDPStrategy)
      local_rank = trainer.strategy.local_rank
      assert trainer.strategy.root_device == torch.device(
          f"cuda:{local_rank}"
      )
  
      model = BoringModelGPU()
  
      trainer.fit(model)
  
      # assert after training, model is moved to CPU and memory is deallocated
      assert model.device == torch.device("cpu")
      cuda_memory = torch.cuda.memory_allocated()
      assert cuda_memory < model.start_cuda_memory
  
imports: import os
  from unittest import mock
  from unittest.mock import Mock
  import lightning.pytorch
  import pytest
  import torch
  from lightning.fabric.plugins.environments import ClusterEnvironment, LightningEnvironment
  from lightning.fabric.utilities.distributed import _distributed_is_initialized
  from lightning.fabric.utilities.imports import _TORCH_GREATER_EQUAL_2_0
  from lightning.pytorch import Trainer
  from lightning.pytorch.callbacks import Callback, EarlyStopping
  from lightning.pytorch.demos.boring_classes import BoringDataModule, BoringModel
  from lightning.pytorch.strategies import DDPStrategy
  from lightning.pytorch.strategies.launchers import _SubprocessScriptLauncher
  from lightning.pytorch.strategies.launchers.multiprocessing import _MultiProcessingLauncher
  from lightning.pytorch.trainer import seed_everything
  from torch.distributed.optim import ZeroRedundancyOptimizer
  from torch.multiprocessing import ProcessRaisedException
  from torch.nn.parallel.distributed import DistributedDataParallel
  import tests_pytorch.helpers.pipelines
  from tests_pytorch.helpers.datamodules import ClassifDataModule
  from tests_pytorch.helpers.runif import RunIf
  from tests_pytorch.helpers.simple_models import ClassificationModel
label_desc: Use image node_id 16 for calling a global function with example usage: test_ddp_with_2_gpus() without return types