fix test.

Author: GdoongMathew

src/lightning/pytorch/accelerators/mps.py

@@ -93,17 +93,21 @@ def register_accelerators(cls, accelerator_registry: _AcceleratorRegistry) -> No
     def device_name(cls, device: Optional[_DEVICE] = None) -> str:
         if not cls.is_available():
             return ""
-        try:
-            result = subprocess.run(
-                ["sysctl", "-n", "machdep.cpu.brand_string"],
-                capture_output=True,
-                text=True,
-                check=True,
-            )
-            result_str = result.stdout.strip()
-        except (subprocess.SubprocessError, FileNotFoundError):
-            result_str = "True (mps)"
-        return result_str
+        return _get_mps_device_name()
+
+
+def _get_mps_device_name() -> str:
+    try:
+        result = subprocess.run(
+            ["sysctl", "-n", "machdep.cpu.brand_string"],
+            capture_output=True,
+            text=True,
+            check=True,
+        )
+        result_str = result.stdout.strip()
+    except subprocess.SubprocessError:
+        result_str = "True (mps)"
+    return result_str
 
 
 # device metrics

tests/tests_pytorch/conftest.py

@@ -208,6 +208,9 @@ def cuda_count_4(monkeypatch):
 def mock_mps_count(monkeypatch, n: int) -> None:
     monkeypatch.setattr(lightning.fabric.accelerators.mps, "_get_all_available_mps_gpus", lambda: [0] if n > 0 else [])
     monkeypatch.setattr(lightning.fabric.accelerators.mps.MPSAccelerator, "is_available", lambda *_: n > 0)
+    monkeypatch.setattr(
+        lightning.pytorch.accelerators.mps, "_get_mps_device_name", lambda: "Mocked MPS Device" if n > 0 else ""
+    )
 
 
 @pytest.fixture