diff -r acb30ed7eceb Lib/test/test_warnings.py
--- a/Lib/test/test_warnings.py	Wed Aug 13 09:36:06 2014 +0300
+++ b/Lib/test/test_warnings.py	Fri Aug 15 17:17:10 2014 -0400
@@ -61,6 +61,25 @@
         sys.modules['warnings'] = original_warnings
         super(BaseTest, self).tearDown()
 
+class PublicAPITests(BaseTest):
+
+    """Ensures that the correct values are exposed in the
+    public API.
+    """
+
+    def test_module_all_attribute(self):
+        self.assertTrue(hasattr(self.module, '__all__'))
+        target_api = ["warn", "warn_explicit", "showwarning",
+                      "formatwarning", "filterwarnings", "simplefilter",
+                      "resetwarnings", "catch_warnings"]
+        self.assertSetEqual(set(self.module.__all__),
+                            set(target_api))
+
+class CPublicAPITests(PublicAPITests, unittest.TestCase):
+    module = c_warnings
+
+class PyPublicAPITests(PublicAPITests, unittest.TestCase):
+    module = py_warnings
 
 class FilterTests(BaseTest):
 
diff -r acb30ed7eceb Lib/warnings.py
--- a/Lib/warnings.py	Wed Aug 13 09:36:06 2014 +0300
+++ b/Lib/warnings.py	Fri Aug 15 17:17:10 2014 -0400
@@ -2,7 +2,8 @@
 
 import sys
 
-__all__ = ["warn", "showwarning", "formatwarning", "filterwarnings",
+__all__ = ["warn", "warn_explicit", "showwarning",
+           "formatwarning", "filterwarnings", "simplefilter",
            "resetwarnings", "catch_warnings"]