class_docstr: A wrapper class for testing core utils functions
code: def test_masked_mean(self):
      self.assertEqual(
          torch.mean(self.test_input_unmasked),
          masked_mean(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 2 for calling the CoreTester obj's underlying member method code with example usage: obj.test_masked_mean() without return types