code: def test_gradcheck(self, device):
      patches = torch.rand(2, 1, 16, 16, device=device)
      patches = utils.tensor_to_gradcheck_var(patches)  # to var
      keynet = KeyNet().to(patches.device, patches.dtype)
      assert gradcheck(
          keynet,
          (patches,),
          eps=1e-4,
          atol=1e-4,
          nondet_tol=1e-8,
          raise_exception=True,
          fast_mode=True,
      )
  
file_path: kornia/test/feature/test_keynet.py
imports: import torch
  from torch.autograd import gradcheck
  import kornia.testing
  from kornia.feature import KeyNet
label_desc: Use image node_id 3 for calling the TestKeyNet obj's underlying member method code with example usage: obj.test_gradcheck(device) without return types