tests: shortcut is_using_postgresql() to make sure the right mode is used

tests/utilities.py

@@ -57,9 +57,11 @@ def create_temporary_pub(sql_mode=False):
     if sql_mode:
         pub.user_class = sql.SqlUser
         pub.tracking_code_class = sql.TrackingCode
+        pub.is_using_postgresql = lambda: True
     else:
         pub.user_class = User
         pub.tracking_code_class = TrackingCode
+        pub.is_using_postgresql = lambda: False
 
     if os.path.exists(pub.app_dir):
         pub.cfg = {}