Fix Windows task and certificate collector reliability

tests/test_windows.py

@@ -155,6 +155,19 @@ class FakeProcess:
 
 
 class ProcessTests(unittest.TestCase):
+    def test_serialization_exit_and_diagnostic_switch(self):
+        def create(args, **kwargs):
+            self.assertIn('-Diagnostic', args)
+            process = FakeProcess(args, **kwargs)
+            process.returncode = 3
+            kwargs['stdout'].write(b'SECRET')
+            return process
+        with patch('samsara.collectors.windows.subprocess.Popen', side_effect=create):
+            with self.assertRaises(WindowsCollectionError) as error:
+                run_section('tasks', 'powershell.exe', diagnostic=True)
+            self.assertEqual(error.exception.code, 'serialization_failed')
+            self.assertNotIn('SECRET', str(error.exception))
+
     def test_timeout_and_cancel_kill_and_reap_without_shell(self):
         for cancel in [False,True]:
             processes=[]