Issue #7849: Now the utility ``check_warnings`` verifies if the warnings are
effectively raised.  A new utility ``check_py3k_warnings`` deals with py3k warnings.
diff --git a/Lib/test/string_tests.py b/Lib/test/string_tests.py
index db0571f..7cfe65b 100644
--- a/Lib/test/string_tests.py
+++ b/Lib/test/string_tests.py
@@ -715,8 +715,7 @@
         EQ("bobobXbobob", "bobobobXbobobob", "replace", "bobob", "bob")
         EQ("BOBOBOB", "BOBOBOB", "replace", "bob", "bobby")
 
-        # Silence Py3k warning
-        with test_support.check_warnings():
+        with test_support.check_py3k_warnings():
             ba = buffer('a')
             bb = buffer('b')
         EQ("bbc", "abc", "replace", ba, bb)