code: def test_retain_grad_hidden_states_attentions(self):
      # longformer cannot keep gradients in attentions or hidden states
      return
  
imports: import unittest
  from transformers import LongformerConfig, is_torch_available
  from transformers.testing_utils import require_sentencepiece, require_tokenizers, require_torch, slow, torch_device
  from ...test_configuration_common import ConfigTester
  from ...test_modeling_common import ModelTesterMixin, ids_tensor, random_attention_mask
  from ...test_pipeline_mixin import PipelineTesterMixin
label_desc: Use image node_id 12 for calling the LongformerModelTest obj's underlying member method code with example usage: obj.test_retain_grad_hidden_states_attentions() without return types