skip test for Windows

tests/plugins/test_custom_plugin.py

@@ -1,17 +1,21 @@
 import pytest
 import torch
+
 from pytorch_lightning import Trainer
 from pytorch_lightning.plugins import DDPPlugin
 from tests.helpers import BoringModel
+from tests.helpers.runif import RunIf
 
 
 class CustomParallelPlugin(DDPPlugin):
+
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
         # Set to None so it will be overwritten by the accelerator connector.
         self.sync_batchnorm = None
 
 
+@RunIf(skip_windows=True)
 @pytest.mark.skipif(torch.cuda.is_available(), reason="test doesn't requires GPU machine")
 def test_sync_batchnorm_set(tmpdir):
     """Tests if sync_batchnorm is automatically set for custom plugin."""