TST(yaml-model-parser): updated test to new behavior

unittests/test_data_model.py

@@ -44,7 +44,10 @@ RT1:
         """
         model_recursive = parse_model_from_string(model_recursive_str)
         prop1 = model_recursive["RT1"].get_property("RT1")
-        assert prop1.datatype is None
+
+        assert prop1.datatype is not None
+        assert prop1.datatype == "RT1"
+
         # TODO The next line actually changes model_recursive in place, is this OK?
         RT1 = model_recursive.get_deep("RT1")
         assert model_recursive["RT1"] == RT1