Address PR comments: refactor test to use boring classes and clarify assertion

Author: littlebullGit

tests/tests_pytorch/callbacks/test_model_checkpoint_additional_cases.py

@@ -212,40 +212,7 @@ def test_model_checkpoint_save_last_link_symlink_bug(tmp_path):
     """Reproduce the bug where save_last='link' and save_top_k=-1 creates a recursive symlink."""
     import os
 
-    class RandomDataset(Dataset):
-        def __init__(self, size, length):
-            self.len = length
-            self.data = torch.randn(length, size)
-
-        def __getitem__(self, index):
-            return self.data[index]
-
-        def __len__(self):
-            return self.len
-
-    class BoringModel(LightningModule):
-        def __init__(self):
-            super().__init__()
-            self.layer = torch.nn.Linear(32, 2)
-
-        def forward(self, x):
-            return self.layer(x)
-
-        def training_step(self, batch, batch_idx):
-            loss = self(batch).sum()
-            self.log("train_loss", loss)
-            return {"loss": loss}
-
-        def validation_step(self, batch, batch_idx):
-            loss = self(batch).sum()
-            self.log("valid_loss", loss)
-
-        def test_step(self, batch, batch_idx):
-            loss = self(batch).sum()
-            self.log("test_loss", loss)
-
-        def configure_optimizers(self):
-            return torch.optim.SGD(self.layer.parameters(), lr=0.1)
+    from lightning.pytorch.demos.boring_classes import BoringModel
 
     trainer = Trainer(
         default_root_dir=tmp_path,
@@ -257,10 +224,10 @@ def configure_optimizers(self):
     )
 
     model = BoringModel()
-    trainer.fit(model, train_dataloaders=DataLoader(RandomDataset(32, 64), batch_size=2))
+    trainer.fit(model)
 
     last_ckpt = tmp_path / "last.ckpt"
     assert last_ckpt.exists()
-    # With the fix, it should not be a symlink to itself
+    # With the fix, if a symlink exists, it should not point to itself (preventing recursion)
     if os.path.islink(str(last_ckpt)):
         assert os.readlink(str(last_ckpt)) != str(last_ckpt)