code: def test_save_checkpoint_wrong_format(self, _):
      torchmodel = Mock()
      optim = Mock()
      state = {
          torchbearer.SELF: Trial(torchmodel, optim, None, []),
          torchbearer.METRICS: {"test_metric": 0.001},
          torchbearer.EPOCH: 2,
      }
  
      file_format = "test_file_{test_metric:d}.pt"
      check = _Checkpointer(file_format)
      try:
          check.save_checkpoint(state)
      except:
          return
  
      self.fail(
          "No error was thrown when wrong format chosen for save file format"
      )
  
imports: from unittest import TestCase
  from mock import patch, Mock
  import torchbearer
  from torchbearer import Trial
  from torchbearer.callbacks.checkpointers import _Checkpointer, ModelCheckpoint, MostRecent, Interval, Best
  import warnings
label_desc: Use image node_id 8 for calling the TestCheckpointer obj's underlying member method code with example usage: obj.test_save_checkpoint_wrong_format(_) without return types