code: def test_load_optimizer(backend):
      """
      Test _load_optimizer_config with a pytorch optimizer, when the `torch.optim.Optimizer` class name is specified.
      For pytorch, we expect a `torch.optim` class to be returned.
      """
      class_name = "Adam"
      cfg_opt = {"class_name": class_name}
      optimizer = _load_optimizer_config(cfg_opt, backend=backend)
      assert optimizer.__name__ == class_name
      assert isinstance(optimizer, type)
  
file_path: alibi-detect/alibi_detect/saving/_pytorch/tests/test_saving_pt.py
imports: from pytest_cases import param_fixture, parametrize, parametrize_with_cases
  from alibi_detect.saving.tests.datasets import ContinuousData
  from alibi_detect.saving.tests.models import encoder_model
  from alibi_detect.cd.pytorch import HiddenOutput
  from alibi_detect.saving.loading import _load_model_config, _load_optimizer_config
  from alibi_detect.saving.saving import _path2str, _save_model_config
  from alibi_detect.saving._pytorch.saving import save_device
  from alibi_detect.saving.schemas import ModelConfig
  import torch
label_desc: Use image node_id 1 for calling a global function with example usage: test_load_optimizer(backend) without return types