code: def test__cpu(self) -> None:
      self._test__accelerator(accelerator="cpu", expected_device="cpu")
  
imports: from typing import Tuple
  import pytest
  import torch
  from pytest_mock import MockerFixture
  from pytorch_lightning import Trainer
  from torch import Tensor, nn
  from torch.utils.data import DataLoader, Dataset
  from lightly.utils.benchmarking import KNNClassifier
  from lightly.utils.benchmarking.knn_classifier import F
label_desc: Use image node_id 2 for calling the TestKNNClassifier obj's underlying member method code with example usage: obj.test__cpu() without return types