Add test for ReadOnly

Author: chadwhitacre

tests.py

@@ -5,6 +5,7 @@
 from unittest import TestCase
 
 from postgres import Postgres, TooFew, TooMany
+from postgres.orm import ReadOnly
 from psycopg2.extras import RealDictCursor
 from psycopg2 import InterfaceError, ProgrammingError
 
@@ -250,6 +251,12 @@ def test_updating_attributes_works(self):
         bar = self.db.one("SELECT bar FROM foo WHERE bar='blah'")
         assert bar == one.bar
 
+    def test_attributes_are_read_only(self):
+        one = self.db.one("SELECT foo.*::foo FROM foo WHERE bar='baz'")
+        def assign():
+            one.bar = "blah"
+        self.assertRaises(ReadOnly, assign)
+
 
 # cursor_factory
 # ==============