Check device count before running dist tests (#2799)

* Check device count before running dist tests

* fixing format for "Check device count before running dist tests"

* Check device count against max world size

* Check GPU count before launching dist tests

* double-check GPU actually exists

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Co-authored-by: NOlatunji Ruwase <olruwase@microsoft.com>
Co-authored-by: NJeff Rasley <jerasley@microsoft.com>
Co-authored-by: NMichael Wyatt <michaelwyatt@microsoft.com>

tests/unit/common.py

@@ -108,6 +108,10 @@ class DistributedExec(ABC):
         return fixture_kwargs
 
     def _launch_procs(self, num_procs):
+        if torch.cuda.is_available() and torch.cuda.device_count() < num_procs:
+            pytest.skip(
+                f"Skipping test because not enough GPUs are available: {num_procs} required, {torch.cuda.device_count()} available"
+            )
         mp.set_start_method('forkserver', force=True)
         skip_msg = mp.Queue()  # Allows forked processes to share pytest.skip reason
         processes = []