code: def test_default_for_key_metric(self):
      metric = metrics.Loss()
      metric = default_for_key("test")(metric)
      self.assertTrue(metrics.get_default("test").name == "loss")
      self.assertTrue(metric.name == "loss")
  
imports: import unittest
  from mock import Mock
  import torchbearer.metrics
  from torchbearer.metrics import default_for_key, lambda_metric, EpochLambda, BatchLambda
label_desc: Use image node_id 2 for calling the TestDecorators obj's underlying member method code with example usage: obj.test_default_for_key_metric() without return types