diff -r 5f0d1aad7322 Lib/unittest/case.py
--- a/Lib/unittest/case.py	Wed Dec 04 00:41:24 2013 +0100
+++ b/Lib/unittest/case.py	Wed Dec 04 01:11:20 2013 +0100
@@ -69,6 +69,9 @@ class _Outcome(object):
             else:
                 self.success = False
                 self.errors.append((test_case, exc_info))
+            # explicitly break a reference cycle:
+            # exc_info -> frame -> exc_info
+            exc_info = None
         else:
             if self.result_supports_subtests and self.success:
                 self.errors.append((test_case, None))
@@ -577,6 +580,9 @@ class TestCase(object):
             for test, reason in outcome.skipped:
                 self._addSkip(result, test, reason)
             self._feedErrorsToResult(result, outcome.errors)
+            # explicitly break a reference cycle:
+            # outcome.errors -> frame -> outcome -> outcome.errors
+            outcome.errors.clear()
             if outcome.success:
                 if expecting_failure:
                     if outcome.expectedFailure:
diff -r 5f0d1aad7322 Lib/unittest/test/test_case.py
--- a/Lib/unittest/test/test_case.py	Wed Dec 04 00:41:24 2013 +0100
+++ b/Lib/unittest/test/test_case.py	Wed Dec 04 01:11:20 2013 +0100
@@ -1533,6 +1533,26 @@ test case
             del case
             self.assertFalse(wr())
 
+    def test_no_exception_leak(self):
+        # Issue #19880: TestCase.run() should not keep a reference
+        # to the exception
+        class MyException(Exception):
+            ninstance = 0
+
+            def __init__(self):
+                MyException.ninstance += 1
+                Exception.__init__(self)
+
+            def __del__(self):
+                MyException.ninstance -= 1
+
+        def raise_exc():
+            raise MyException()
+
+        test = unittest.FunctionTestCase(raise_exc)
+        test.run()
+        self.assertEqual(MyException.ninstance, 0)
+
 
 if __name__ == "__main__":
     unittest.main()