Fix missing docs (Lightning-AI#2659)

* dataloader_idx typo

* typo

* update test_step docs

* missing optimizer_idx

Author: rohitgr7

.github/BECOMING_A_CORE_CONTRIBUTOR.md

@@ -11,7 +11,7 @@ First and foremost, you'll be evaluated against [these core values](https://gith
 ### The bar for joining the team   
 Lightning is being used to solve really hard problems at the top AI labs in the world. As such, the bar for adding team members is extremely high. Candidates must have solid engineering skills, have a good eye for user experience, and must be a power user of Lightning and PyTorch.
 
-With that said, the Lightning team will be diverse and a reflection of an inclusive AI community. You don't have to be an engineer to conntribute! Scientists with great usability intuition and PyTorch ninja skills are welcomed!
+With that said, the Lightning team will be diverse and a reflection of an inclusive AI community. You don't have to be an engineer to contribute! Scientists with great usability intuition and PyTorch ninja skills are welcomed!
 
 ### Responsibilities:
 The responsibilities mainly revolve around 3 things.

docs/source/introduction_guide.rst

@@ -903,7 +903,7 @@ With your own
 
     class LitMNIST(LightningModule):
 
-        def backward(self, use_amp, loss, optimizer):
+        def backward(self, use_amp, loss, optimizer, optimizer_idx):
             # do a custom way of backward
             loss.backward(retain_graph=True)
 

pytorch_lightning/core/lightning.py

@@ -470,8 +470,8 @@ def validation_step(self, batch, batch_idx):
             .. code-block:: python
 
                 # CASE 2: multiple validation datasets
-                def validation_step(self, batch, batch_idx, dataset_idx):
-                    # dataset_idx tells you which dataset this is.
+                def validation_step(self, batch, batch_idx, dataloader_idx):
+                    # dataloader_idx tells you which dataset this is.
 
         Note:
             If you don't need to validate you don't need to implement this method.
@@ -698,8 +698,8 @@ def test_step(self, batch, batch_idx):
             .. code-block:: python
 
                 # CASE 2: multiple test datasets
-                def test_step(self, batch, batch_idx, dataset_idx):
-                    # dataset_idx tells you which dataset this is.
+                def test_step(self, batch, batch_idx, dataloader_idx):
+                    # dataloader_idx tells you which dataset this is.
 
         Note:
             If you don't need to validate you don't need to implement this method.
@@ -1426,10 +1426,17 @@ def test_dataloader(self):
 
                     return loader
 
+                # can also return multiple dataloaders
+                def test_dataloader(self):
+                    return [loader_a, loader_b, ..., loader_n]
+
         Note:
             If you don't need a test dataset and a :meth:`test_step`, you don't need to implement
             this method.
 
+        Note:
+            In the case where you return multiple test dataloaders, the :meth:`test_step`
+            will have an argument ``dataloader_idx`` which matches the order here.
         """
 
     def val_dataloader(self) -> Union[DataLoader, List[DataLoader]]:
@@ -1481,7 +1488,7 @@ def val_dataloader(self):
 
         Note:
             In the case where you return multiple validation dataloaders, the :meth:`validation_step`
-            will have an argument ``dataset_idx`` which matches the order here.
+            will have an argument ``dataloader_idx`` which matches the order here.
         """
 
     def summarize(self, mode: str = ModelSummary.MODE_DEFAULT) -> ModelSummary: