test for complicated batch structure (#3928)

* test for complicated batch structure

* test for complicated batch structure

tests/trainer/logging/test_train_loop_logging_1_0.py

@@ -8,6 +8,7 @@ import pytest
 
 from pytorch_lightning import Trainer
 from tests.base.deterministic_model import DeterministicModel
+from torch.utils.data import Dataset
 
 
 def test__training_step__log(tmpdir):
@@ -419,3 +420,56 @@ def test_validation_step_with_string_data_logging():
         weights_summary=None,
     )
     trainer.fit(model, train_data, val_data)
+
+
+def test_nested_datasouce_batch(tmpdir):
+
+    class NestedDictStringDataset(Dataset):
+        def __init__(self, size, length):
+            self.len = length
+            self.data = torch.randn(length, size)
+
+        def __getitem__(self, index):
+            x = {
+                'post_text': ['bird is fast', 'big cat'],
+                'dense_0': [
+                    torch.tensor([-0.1000,  0.2000], dtype=torch.float64),
+                    torch.tensor([1, 1], dtype=torch.uint8)
+                ],
+                'post_id': ['115', '116'],
+                'label': [torch.tensor([0, 1]), torch.tensor([1, 1], dtype=torch.uint8)]
+            }
+            return x
+
+        def __len__(self):
+            return self.len
+
+    class TestModel(BoringModel):
+        def on_train_epoch_start(self) -> None:
+            print("override any method to prove your bug")
+
+        def training_step(self, batch, batch_idx):
+            output = self.layer(torch.rand(32))
+            loss = self.loss(batch, output)
+            return {"loss": loss}
+
+        def validation_step(self, batch, batch_idx):
+            output = self.layer(torch.rand(32))
+            loss = self.loss(batch, output)
+            self.log("x", loss)
+            return {"x": loss}
+
+    # fake data
+    train_data = torch.utils.data.DataLoader(NestedDictStringDataset(32, 64))
+    val_data = torch.utils.data.DataLoader(NestedDictStringDataset(32, 64))
+
+    # model
+    model = TestModel()
+    trainer = Trainer(
+        default_root_dir=os.getcwd(),
+        limit_train_batches=1,
+        limit_val_batches=1,
+        max_epochs=1,
+        weights_summary=None,
+    )
+    trainer.fit(model, train_data, val_data)