import callback to checkpoint test file

Author: vsey

tests/tests_pytorch/checkpointing/test_model_checkpoint.py

@@ -35,7 +35,7 @@
 import lightning.pytorch as pl
 from lightning.fabric.utilities.cloud_io import _load as pl_load
 from lightning.pytorch import Trainer, seed_everything
-from lightning.pytorch.callbacks import ModelCheckpoint
+from lightning.pytorch.callbacks import Callback, ModelCheckpoint
 from lightning.pytorch.demos.boring_classes import BoringModel, RandomIterableDataset
 from lightning.pytorch.loggers import CSVLogger, TensorBoardLogger
 from lightning.pytorch.utilities.exceptions import MisconfigurationException