return None if cpu_count() is undetermined + add mock test

1 files changed, 8 insertions, 0 deletions

diff --git a/psutil/tests/test_windows.py b/psutil/tests/test_windows.py
index 32c46f67..252201c5 100755
--- a/psutil/tests/test_windows.py
+++ b/psutil/tests/test_windows.py
@@ -92,6 +92,14 @@ class TestSystemAPIs(unittest.TestCase):
         psutil_value = psutil.cpu_count()
         self.assertEqual(sys_value, psutil_value)
 
+    def test_cpu_count_mocked(self):
+        # Emulate a case where the C extension is unable to determine
+        # CPU count.
+        with mock.patch('psutil._pswindows.cext.cpu_count',
+                        return_value=(0, 0)):
+            self.assertIsNone(psutil.cpu_count(logical=True))
+            self.assertIsNone(psutil.cpu_count(logical=False))
+
     def test_cpu_freq(self):
         w = wmi.WMI()
         proc = w.Win32_Processor()[0]