code: def test_no_existing_file(self, mock_dirs, mock_save):
      check = _Checkpointer(
          "thisdirectoryshouldntexist/norshouldthis/model.pt"
      )
      check.most_recent = "thisfiledoesnotexist.pt"
      with warnings.catch_warnings(record=True) as w:
          warnings.simplefilter("always")
          check.save_checkpoint(
              {torchbearer.METRICS: {}, torchbearer.SELF: Mock()}, True
          )
          self.assertTrue(len(w) == 1)
          self.assertTrue(
              "Failed to delete old file" in str(w[-1].message)
          )
  
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 2 for calling the TestCheckpointer obj's underlying member method code with example usage: obj.test_no_existing_file(mock_dirs, mock_save) without return types