code: def test_activate_requires_grad(self):
      model = nn.Sequential(
          nn.Linear(32, 32),
          nn.ReLU(),
      )
      self.assertTrue(has_grad(model))
      deactivate_requires_grad(model)
      self.assertFalse(has_grad(model))
      activate_requires_grad(model)
      self.assertTrue(has_grad(model))
  
imports: import copy
  import unittest
  import torch
  import torch.nn
  from lightly.models import utils
  from lightly.models.utils import _no_grad_trunc_normal, activate_requires_grad, batch_shuffle, batch_unshuffle, deactivate_requires_grad, nearest_neighbors, normalize_weight, update_momentum
label_desc: Use image node_id 3 for calling the TestModelUtils obj's underlying member method code with example usage: obj.test_activate_requires_grad() without return types