code: def test_single_device_default_device():
      assert SingleDeviceStrategy().root_device == torch.device("cpu")
  
file_path: pytorch-lightning/tests/tests_fabric/strategies/test_single_device.py
imports: from unittest.mock import Mock
  import pytest
  import torch
  from lightning.fabric import Fabric
  from lightning.fabric.strategies import SingleDeviceStrategy
  from tests_fabric.helpers.runif import RunIf
label_desc: Use image node_id 1 for calling a global function with example usage: test_single_device_default_device() without return types