Add separator to exception message in ScalarListType

sqlalchemy_utils/types/scalar_list.py

@@ -67,6 +67,7 @@ class ScalarListType(types.TypeDecorator):
                     "List values can't contain string '%s' (its being used as "
                     "separator. If you wish for scalar list values to contain "
                     "these strings, use a different separator string.)"
+                    % self.separator
                 )
             return self.separator.join(
                 map(six.text_type, value)

tests/types/test_scalar_list.py

@@ -47,8 +47,14 @@ class TestScalarUnicodeList(TestCase):
         )
 
         self.session.add(user)
-        with raises(sa.exc.StatementError):
+        with raises(sa.exc.StatementError) as db_err:
             self.session.commit()
+        print db_err.value.message
+        assert (
+            "List values can't contain string ',' (its being used as "
+            "separator. If you wish for scalar list values to contain "
+            "these strings, use a different separator string.)"
+        ) in db_err.value.message
 
     def test_save_unicode_list(self):
         user = self.User(