diff -r f2c7f771bf6a Lib/unittest/case.py
--- a/Lib/unittest/case.py	Tue Dec 03 19:17:25 2013 +0100
+++ b/Lib/unittest/case.py	Tue Dec 03 23:37:16 2013 +0100
@@ -69,6 +69,7 @@ class _Outcome(object):
             else:
                 self.success = False
                 self.errors.append((test_case, exc_info))
+            exc_info = None
         else:
             if self.result_supports_subtests and self.success:
                 self.errors.append((test_case, None))
@@ -585,6 +586,9 @@ class TestCase(object):
                         self._addUnexpectedSuccess(result)
                 else:
                     result.addSuccess(self)
+            outcome.errors.clear()
+            self._outcome = None
+            outcome = None
             return result
         finally:
             result.stopTest(self)