addSubTest(test, subtest, outcome)
Called when a subtest finishes. test is the test case corresponding to the test method. subtest is a custom TestCase instance describing the subtest.
If outcome is None, the subtest succeeded. Otherwise, it failed with an exception where outcome is a tuple of the form returned by sys.exc_info(): (type, value, traceback).
The default implementation does nothing when the outcome is a success, and records subtest failures as normal failures.
New in version 3.