def test_singleSynchronousSuccess(self):
        """
        When given a callable that succeeds without returning a Deferred,
        include the return value in the results list, tagged with a SUCCESS
        flag.
        """
        d = util._runSequentially([lambda: None])
        self.assertDeferredResult(d, self.assertEqual, [(defer.SUCCESS, None)])

        When given a callable that succeeds without returning a Deferred,
        include the return value in the results list, tagged with a SUCCESS
        flag.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/test/test_util.py