Add ddp launcher for ddp testing

tests/trainer/properties/test_get_model.py

@@ -17,6 +17,7 @@ import pytest
 import torch
 
 from pytorch_lightning import Trainer
+from tests.backends.launcher import DDPLauncher
 from tests.base.boring_model import BoringModel
 
 
@@ -86,7 +87,10 @@ def test_get_model_gpu(tmpdir):
 
 @pytest.mark.skipif(not torch.cuda.is_available(), reason="test requires GPU machine")
 @pytest.mark.skipif(sys.platform == "win32", reason="DDP not available on windows")
-def test_get_model_ddp_gpu(tmpdir):
+@DDPLauncher.run("--accelerator [accelerator]",
+                 max_epochs=["1"],
+                 accelerator=["ddp", "ddp_spawn"])
+def test_get_model_ddp_gpu(tmpdir, args=None):
     """
     Tests that :meth:`trainer.get_model` extracts the model correctly when using GPU + ddp accelerators
     """
@@ -100,6 +104,7 @@ def test_get_model_ddp_gpu(tmpdir):
         limit_val_batches=2,
         max_epochs=1,
         gpus=1,
-        accelerator='ddp_spawn'
+        accelerator=args.accelerator
     )
     trainer.fit(model)
+    return 1