Extra check on result list

tests/test_reference_model.py

@@ -38,6 +38,7 @@ class TestReferenceModel(unittest.TestCase):
         result_list = instance.get_result()
         self.assertIsNotNone(result_list)
         last_result = result_list[len(result_list)-1]
+        self.assertIsNotNone(result_list[0].valid_time_start)
         self.assertEqual(555.8507083333333, last_result.all_values["TMDD"])
 
     def test_get_model_id(self):