def METHOD_NAME(self) -> defer.Deferred:
    async def testfunc() -> None:
        self._check_test_key("one")
        d = Clock(reactor).sleep(0)
        self.assertIs(current_context(), SENTINEL_CONTEXT)
        await d
        self._check_test_key("one")
    return self._test_run_in_background(testfunc)