Replace catch_warnings with check_warnings when it makes sense.  Use assertRaises context manager to simplify some tests.
diff --git a/Lib/test/test_urllibnet.py b/Lib/test/test_urllibnet.py
index 77b5445..8eb01e5 100644
--- a/Lib/test/test_urllibnet.py
+++ b/Lib/test/test_urllibnet.py
@@ -182,10 +182,8 @@
 
 def test_main():
     test_support.requires('network')
-    from warnings import filterwarnings, catch_warnings
-    with catch_warnings():
-        filterwarnings('ignore', '.*urllib\.urlopen.*Python 3.0',
-                        DeprecationWarning)
+    with test_support.check_py3k_warnings(
+            ("urllib.urlopen.. has been removed", DeprecationWarning)):
         test_support.run_unittest(URLTimeoutTest,
                                   urlopenNetworkTests,
                                   urlretrieveNetworkTests)