REVIEW: fix tests

unittests/test_add_property.py

@@ -199,14 +199,16 @@ def test_property_parameter_with_entity_and_datatype():
     assert concrete_property.value is None
     assert concrete_property.datatype == db.INTEGER
 
-    concrete_property.datatype = None
+    concrete_property.datatype = db.DOUBLE
     concrete_property.value = 3.14
 
     with raises(ValueError):
         # cannot parse 3.14 to integer
         concrete_property.datatype = db.INTEGER
-    concrete_property.datatype = None
-    concrete_property.value = 3.14
+
+    # nothing should've changed after the ValueError
+    assert concrete_property.datatype == db.DOUBLE
+    assert concrete_property.value == 3.14
 
 
 def test_kw_name_and_value():