--- a/tests/unit.py	Mon Apr 30 13:21:48 2012 -0700
+++ b/tests/unit.py	Tue May 01 10:33:37 2012 -0700
@@ -59,6 +59,10 @@
                   'activeTests':  ['ts']}
         example(config)
         config['test_timeout'] = 1200 # default
+        config['preferences'] = {"browser.bookmarks.max_backups": 0,
+                                 "browser.cache.disk.smart_size.enabled": False}
+
+        # ensure they are equal
         self.assertEqual(config, example.config)
         example.serialize(filename)
         self.assertTrue(os.path.exists(filename))
@@ -101,6 +105,7 @@
             missingvalueexception = e
         self.assertTrue(isinstance(e, configuration.MissingValueException))
 
+
     def test_multiple_configurations(self):
         """test having multiple configurations"""
 
@@ -141,5 +146,25 @@
         config['test_timeout'] = 1200
         self.assertEqual(example.config, config)
 
+    def test_extend(self):
+
+        # default preferences
+        example = ExampleConfiguration()
+        default_prefs = {"browser.bookmarks.max_backups": 0,
+                         "browser.cache.disk.smart_size.enabled": False}
+        example.parse_args(['-a', 'ts', '-e', '/opt/bin/firefox'])
+        self.assertEqual(example.config['preferences'], default_prefs)
+
+        # now extend them
+        example = ExampleConfiguration()
+        default_prefs['network.dns.ipv4OnlyDomains'] = 'localhost'
+        tf = tempfile.mktemp()
+        f = file(tf, 'w')
+        f.write(json.dumps({'preferences': {'network.dns.ipv4OnlyDomains': 'localhost'}}))
+        f.close()
+        example.parse_args(['-a', 'ts', '-e', '/opt/bin/firefox', tf])
+        self.assertEqual(example.config['preferences'], default_prefs)
+        os.remove(tf)
+
 if __name__ == '__main__':
     unittest.main()