class_docstr: A wrapper class for testing core utils functions
code: def test_masked_var(self):
      self.assertEqual(
          torch.var(self.test_input_unmasked),
          masked_var(self.test_input, self.test_mask),
      )
  
file_path: trl/tests/test_core.py
imports: import unittest
  import torch
  from trl.core import masked_mean, masked_var, masked_whiten, whiten
label_desc: Use image node_id 3 for calling the CoreTester obj's underlying member method code with example usage: obj.test_masked_var() without return types