https://github.com/beanbaginc/diffx/pull/5

--- pydiffx-1.1/pydiffx/tests/testcases.py.orig
+++ pydiffx-1.1/pydiffx/tests/testcases.py
@@ -65,5 +65,5 @@
 
     @contextmanager
     def assertRaisesMessage(self, exception, message):
-        with self.assertRaisesRegexp(exception, re.escape(message)):
+        with self.assertRaises(exception, msg=message):
             yield