[pygobject] Add null_gerror_callback unit test

[Martin Pitt <martinpitt src gnome org>]

commit 4ea37c606f67df843788261b2c8acd6bac4c1e0c
Author: Paolo Borelli <pborelli gnome org>
Date:   Sun Feb 5 18:51:53 2012 +0100

    Add null_gerror_callback unit test
    
    This models the case where the callback is successful and does not set
    an error.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=669415

 tests/test_everything.py |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)
---
diff --git a/tests/test_everything.py b/tests/test_everything.py
index 02447fa..82edfcf 100644
--- a/tests/test_everything.py
+++ b/tests/test_everything.py
@@ -362,6 +362,15 @@ class TestCallbacks(unittest.TestCase):
         Everything.test_gerror_callback(callback)
         self.assertTrue(TestCallbacks.called)
 
+    def test_callback_null_gerror(self):
+        def callback(error):
+            self.assertEqual(error, None)
+            TestCallbacks.called = True
+
+        TestCallbacks.called = False
+        Everything.test_null_gerror_callback(callback)
+        self.assertTrue(TestCallbacks.called)
+
     def test_callback_owned_gerror(self):
         def callback(error):
             self.assertEqual(error.message, 'regression test owned error')