Exception Chaining missing method for suppressing context

Lib/test/test_exceptions.py

 # Python test set -- part 5, built-in exceptions
 
 import os
 import sys
 import unittest
 import pickle
 import weakref
 import errno
 
 from test.support import (TESTFN, unlink, run_unittest, captured_output,
@@ skipping 369 matching lines @@
         except:
             tb = sys.exc_info()[2]
 
         e = Exception()
         e.__traceback__ = tb
         e.__traceback__ = None
         self.assertEqual(e.__traceback__, None)
 
     def testChainingAttrs(self):
         e = Exception()
-        self.assertEqual(e.__context__, None)
-        self.assertEqual(e.__cause__, False)
+        self.assertIsNone(e.__context__)
+        self.assertIs(e.__cause__, Ellipsis)
 
         e = TypeError()
-        self.assertEqual(e.__context__, None)
-        self.assertEqual(e.__cause__, False)
+        self.assertIsNone(e.__context__)
+        self.assertIs(e.__cause__, Ellipsis)
 
         class MyException(EnvironmentError):
             pass
 
         e = MyException()
-        self.assertEqual(e.__context__, None)
-        self.assertEqual(e.__cause__, False)
+        self.assertIsNone(e.__context__)
+        self.assertIs(e.__cause__, Ellipsis)
+
+    def testChainingDescriptors(self):
+        try:
+            raise Exception()
+        except Exception as exc:
+            e = exc
+
+        self.assertIsNone(e.__context__)
+        self.assertIs(e.__cause__, Ellipsis)
+
+        e.__context__ = NameError()
+        e.__cause__ = None
+        self.assertIsInstance(e.__context__, NameError)
+        self.assertIsNone(e.__cause__)
+
+        e.__cause__ = Ellipsis
+        self.assertIs(e.__cause__, Ellipsis)
 
     def testKeywordArgs(self):
         # test that builtin exception don't take keyword args,
         # but user-defined subclasses can if they want
         self.assertRaises(TypeError, BaseException, a=1)
 
         class DerivedException(BaseException):
             def __init__(self, fancy_arg):
                 BaseException.__init__(self)
                 self.fancy_arg = fancy_arg
@@ skipping 470 matching lines @@
         with self.assertRaises(OSError) as cm:
             os.listdir(__file__)
         self.assertEqual(cm.exception.errno, errno.ENOTDIR, cm.exception)
 
 
 def test_main():
     run_unittest(ExceptionTests)
 
 if __name__ == '__main__':
     unittest.main()