code: def test_precision_error(self):
      self.setUp()
      self._std.train()
      val = torch.tensor([0.55])
      for i in range(2):
          self._std.process(val)
  
      result = self._std.process_final({})
      self.assertEqual(0, result)
  
imports: import unittest
  from mock import Mock, call
  from torchbearer.metrics import RunningMean, Metric, RunningMetric, Mean, Std, Var
  import torch
label_desc: Use image node_id 4 for calling the TestStd obj's underlying member method code with example usage: obj.test_precision_error() without return types