diff --git a/docs/source/datamodules.rst b/docs/source/datamodules.rst
index 12b26b4a23857d..8bc7cfc56447bd 100644
--- a/docs/source/datamodules.rst
+++ b/docs/source/datamodules.rst
@@ -13,27 +13,50 @@ matching transforms and data processing/downloads steps required.
 
 .. code-block:: python
 
-    class MNISTDataModule(LightningDataModule):
+    import pytorch_lightning as pl
+    from torch.utils.data import random_split, DataLoader
+
+    # Note - you must have torchvision installed for this example
+    from torchvision.datasets import MNIST
+    from torchvision import transforms
+
+
+    class MNISTDataModule(pl.LightningDataModule):
 
         def __init__(self, data_dir: str = './'):
             super().__init__()
             self.data_dir = data_dir
+            self.transform = transforms.Compose([
+                transforms.ToTensor(),
+                transforms.Normalize((0.1307,), (0.3081,))
+            ])
+
+            # self.dims is returned when you call dm.size()
+            # Setting default dims here because we know them.
+            # Could optionally be assigned dynamically in dm.setup() 
+            self.dims = (1, 28, 28)
 
         def prepare_data(self):
             # download
             MNIST(self.data_dir, train=True, download=True)
             MNIST(self.data_dir, train=False, download=True)
 
-        def setup(self, stage):
+        def setup(self, stage=None):
 
             # Assign train/val datasets for use in dataloaders
-            if stage == 'fit':
-                mnist_full = MNIST(self.data_dir, train=True, download=True)
+            if stage == 'fit' or stage is None:
+                mnist_full = MNIST(self.data_dir, train=True, transform=self.transform)
                 self.mnist_train, self.mnist_val = random_split(mnist_full, [55000, 5000])
 
+                # Optionally...
+                # self.dims = tuple(self.mnist_train[0][0].shape)
+
             # Assign test dataset for use in dataloader(s)
-            if stage == 'test':
-                self.mnist_test = MNIST(self.data_dir, train=False, download=True)
+            if stage == 'test' or stage is None:
+                self.mnist_test = MNIST(self.data_dir, train=False, transform=self.transform)
+
+                # Optionally...
+                # self.dims = tuple(self.mnist_test[0][0].shape)
 
         def train_dataloader(self):
             return DataLoader(self.mnist_train, batch_size=32)
diff --git a/tests/core/test_datamodules.py b/tests/core/test_datamodules.py
index 929c5c3d2c805f..b525a2b344c73d 100644
--- a/tests/core/test_datamodules.py
+++ b/tests/core/test_datamodules.py
@@ -159,6 +159,21 @@ def test_train_val_loop_only(tmpdir):
     assert trainer.callback_metrics['loss'] < 0.6
 
 
+def test_test_loop_only(tmpdir):
+    reset_seed()
+
+    dm = TrialMNISTDataModule(tmpdir)
+
+    model = EvalModelTemplate()
+
+    trainer = Trainer(
+        default_root_dir=tmpdir,
+        max_epochs=3,
+        weights_summary=None,
+    )
+    trainer.test(model, datamodule=dm)
+
+
 def test_full_loop(tmpdir):
     reset_seed()