code: def test_lbm_with_grad(self, device: str):
      self.bias_direction = self.bias_direction.to(
          device
      ).requires_grad_()
      self.evaluation_embeddings = self.evaluation_embeddings.to(
          device
      ).requires_grad_()
      assert self.bias_direction.grad is None
      assert self.evaluation_embeddings.grad is None
  
      lbm = LinearBiasMitigator(requires_grad=True)
      test_bias_mitigated_embeddings = lbm(
          self.evaluation_embeddings, self.bias_direction
      )
      test_bias_mitigated_embeddings.sum().backward()
      assert self.bias_direction.grad is not None
      assert self.evaluation_embeddings.grad is not None
  
imports: import torch
  from torch import allclose
  import pytest
  import json
  from allennlp.common.checks import ConfigurationError
  from allennlp.common.testing import AllenNlpTestCase, multi_device
  from allennlp.fairness.bias_mitigators import LinearBiasMitigator, HardBiasMitigator, INLPBiasMitigator, OSCaRBiasMitigator
  from allennlp.fairness.bias_direction import TwoMeansBiasDirection
label_desc: Use image node_id 4 for calling the LinearBiasMitigatorTest obj's underlying member method code with example usage: obj.test_lbm_with_grad(device) without return types