'Ensure exception does not display a context by default
Wraps unittest.TestCase.assertRaisesRegex'

@contextlib.contextmanager
def assertCleanError(self, exc_type, details, *args):

    if args:
        details = (details % args)
    cm = self.assertRaisesRegex(exc_type, details)
    with cm as exc:
        (yield exc)
    if (exc.exception.__context__ is not None):
        self.assertTrue(exc.exception.__suppress_context__)
