code: def test_reg_l2_called(self):
      self.calibrator.l2_reg = Mock(return_value=torch.Tensor([0]))
      self.calibrator.calibrate(
          self.dataset,
          self.dataset,
          batch_size=10,
          epoch=5,
          use_cuda=False,
          double_fit=False,
          workers=0,
      )
      self.calibrator.l2_reg.assert_called()
  
imports: import unittest
  from unittest.mock import Mock
  import numpy
  import pytest
  import torch
  from torch import nn
  from torch.utils.data import Dataset
  from baal.calibration import DirichletCalibrator
  from baal.modelwrapper import ModelWrapper
label_desc: Use image node_id 4 for calling the CalibrationTest obj's underlying member method code with example usage: obj.test_reg_l2_called() without return types