diff -r 2344e8b7a8aa Doc/library/test.rst
--- a/Doc/library/test.rst	Sun Jun 21 17:12:16 2015 +0300
+++ b/Doc/library/test.rst	Sun Jun 21 18:00:32 2015 +0200
@@ -580,6 +580,43 @@
    .. versionadded:: 3.5
 
 
+.. function:: check__all__(test_instance, module, name_of_module, expected=None, blacklist=None)
+
+   Assert that *module*'s ``__all__`` variable contains all documented names.
+
+   *name_of_module* must be either a string or iterable of strings. One case for
+   the latter is when module imports names from its C backend (e.g. ``csv``,
+   ``_csv``).
+
+   *expected* can be a initial set of module names, that wouldn't otherwise be
+   automatically detected as "documented names" (like objects without proper
+   ``__module__`` attribute).
+
+   *blacklist* can be a set of names that must not be treated as part of
+   documented API even though their names indicate otherwise.
+
+   Example use::
+
+      import unittest
+      from test import support
+      import foo
+
+      class MiscTestCase(unittest.TestCase):
+          def test__all__(self):
+              support.check__all__(self, foo, 'foo')
+
+   Using *expected* and *blacklist*::
+
+      class MiscTestCase(unittest.TestCase):
+          def test__all__(self):
+              expected = {'BAR_CONST', 'FOO_CONST'}
+              blacklist = {'baz'}  # Undocumented name.
+              support.check__all__(self, foo, 'foo', expected=expected,
+                                   blacklist=blacklist)
+
+   .. versionadded:: 3.5
+
+
 The :mod:`test.support` module defines the following classes:
 
 .. class:: TransientResource(exc, **kwargs)
diff -r 2344e8b7a8aa Lib/test/support/__init__.py
--- a/Lib/test/support/__init__.py	Sun Jun 21 17:12:16 2015 +0300
+++ b/Lib/test/support/__init__.py	Sun Jun 21 18:00:32 2015 +0200
@@ -26,6 +26,7 @@
 import sysconfig
 import tempfile
 import time
+import types
 import unittest
 import urllib.error
 import warnings
@@ -89,6 +90,7 @@
     "bigmemtest", "bigaddrspacetest", "cpython_only", "get_attribute",
     "requires_IEEE_754", "skip_unless_xattr", "requires_zlib",
     "anticipate_failure", "load_package_tests", "detect_api_mismatch",
+    "check__all__",
     # sys
     "is_jython", "check_impl_detail",
     # network
@@ -2199,6 +2201,50 @@
     return missing_items
 
 
+def check__all__(test_instance, module, name_of_module, expected=None,
+                 blacklist=None):
+    """Assert that `module`'s __all__ variable contains all documented names.
+
+    name_of_module must be either a string or iterable of strings. One case for
+    the latter is when module imports names from its C backend (e.g. ``csv``,
+    ``_csv``).
+
+    expected can be a initial set of module names, that wouldn't otherwise be
+    automatically detected as "documented names" (like objects without proper
+    __module__ attribute).
+
+    blacklist can be a set of names that must not be treated as part of
+    documented API even though their names indicate otherwise.
+
+    Usage:
+        import unittest
+        from test import support
+        import foo
+
+        class MiscTestCase(unittest.TestCase):
+            def test__all__(self):
+                support.check__all__(self, foo, 'foo')
+
+    """
+    if isinstance(name_of_module, str):
+        name_of_module = (name_of_module, )
+
+    if expected is None:
+        expected = set()
+
+    if blacklist is None:
+        blacklist = set()
+
+    for name in dir(module):
+        if name.startswith('_') or name in blacklist:
+            continue
+        module_object = getattr(module, name)
+        if isinstance(module_object, types.ModuleType):
+            continue
+        if getattr(module_object, '__module__', None) in name_of_module:
+            expected.add(name)
+    test_instance.assertCountEqual(module.__all__, expected)
+
 class SuppressCrashReport:
     """Try to prevent a crash report from popping up.
 
diff -r 2344e8b7a8aa Lib/test/test_support.py
--- a/Lib/test/test_support.py	Sun Jun 21 17:12:16 2015 +0300
+++ b/Lib/test/test_support.py	Sun Jun 21 18:00:32 2015 +0200
@@ -312,6 +312,21 @@
                 self.OtherClass, self.RefClass, ignore=ignore)
         self.assertEqual(set(), missing_items)
 
+    def test_check__all__(self):
+        expected = {'TextTestResult', 'installHandler'}
+        blacklist = {'load_tests', "TestProgram", "BaseTestSuite"}
+        support.check__all__(self,
+                             unittest,
+                             ("unittest", "unittest.result", "unittest.case",
+                              "unittest.suite", "unittest.loader",
+                              "unittest.main", "unittest.runner",
+                              "unittest.signals"),
+                             expected=expected,
+                             blacklist=blacklist)
+
+        self.assertRaises(AssertionError, support.check__all__, self, unittest,
+                          "unittest")
+
     # XXX -follows a list of untested API
     # make_legacy_pyc
     # is_resource_enabled