Fix an error and add a test case

2 files changed, 8 insertions, 2 deletions

diff --git a/test/unittest_testlib.py b/test/unittest_testlib.py
index 2349001..3efaae6 100644
--- a/test/unittest_testlib.py
+++ b/test/unittest_testlib.py
@@ -208,7 +208,11 @@ class TestlibTC(TestCase):
         tc2 = MyTC('test_1')
         self.assertEquals(tc2.datadir, expected_datadir)
         
-
+    def test_is(self):
+        obj_1 = []
+        obj_2 = []
+        self.assertIs(obj_1,obj_1)
+        self.assertRaises(AssertionError, self.assertIs, obj_1, obj_2)
 
 class GenerativeTestsTC(TestCase):
     
diff --git a/testlib.py b/testlib.py
index 1389b96..a158a3c 100644
--- a/testlib.py
+++ b/testlib.py
@@ -1294,7 +1294,9 @@ class TestCase(unittest.TestCase):
 
     def assertIs(self, obj, other, msg=None):
         """compares identity of two reference"""
-        self.assert_(obj is other, "%r is not %r"%(obj, other), msg)
+        if msg is None:
+            msg = "%r is not %r"%(obj, other)
+        self.assert_(obj is other, msg)
 
     def failUnlessRaises(self, excClass, callableObj, *args, **kwargs):
         """override default failUnlessRaise method to return the raised