code: def test_best_case_epoch(self):
      temp_dir = self.get_temp_dir()
      backup_dir = file_utils.join(temp_dir, "subdir")
      self.assertFalse(file_utils.exists(backup_dir))
  
      model = self.make_model()
      self.assertEqual(int(model.layers[0].counter.value), 0)
      cbk = callbacks.BackupAndRestore(
          backup_dir=backup_dir, save_freq="epoch"
      )
  
      x_train = np.random.random((10, 3))
      y_train = np.random.random((10, 1))
  
      try:
          model.fit(
              x_train,
              y_train,
              batch_size=4,
              callbacks=[
                  cbk,
                  InterruptingCallback(steps_int=None, epoch_int=2),
              ],
              epochs=6,
              verbose=0,
          )
      except RuntimeError:
          self.assertEqual(cbk._current_epoch, 1)
          self.assertTrue(file_utils.exists(backup_dir))
          self.assertEqual(int(model.layers[0].counter.value), 6)
  
          hist = model.fit(
              x_train, y_train, batch_size=4, callbacks=[cbk], epochs=5
          )
          self.assertEqual(cbk._current_epoch, 4)
          self.assertEqual(hist.epoch[-1], 4)
          self.assertEqual(int(model.layers[0].counter.value), 21)
  
imports: import numpy
  import pytest
  from keras import callbacks
  from keras import layers
  from keras import testing
  from keras.models import Sequential
  from keras.utils import file_utils
label_desc: Use image node_id 4 for calling the BackupAndRestoreCallbackTest obj's underlying member method code with example usage: obj.test_best_case_epoch() without return types