Method setUp

python/python3/tornado/testing.py:195–238

(self)

        self._test_generator = None  # type: Optional[Union[Generator, Coroutine]]

    def setUp(self) -> None:
        setup_with_context_manager(self, warnings.catch_warnings())
        warnings.filterwarnings(
            "ignore",
            message="There is no current event loop",
            category=DeprecationWarning,
            module=r"tornado\..*",
        )
        super().setUp()
        # NOTE: this code attempts to navigate deprecation warnings introduced
        # in Python 3.10. The idea of an implicit current event loop is
        # deprecated in that version, with the intention that tests like this
        # explicitly create a new event loop and run on it. However, other
        # packages such as pytest-asyncio (as of version 0.16.0) still rely on
        # the implicit current event loop and we want to be compatible with them
        # (even when run on 3.10, but not, of course, on the future version of
        # python that removes the get/set_event_loop methods completely).
        #
        # Deprecation warnings were introduced inconsistently:
        # asyncio.get_event_loop warns, but
        # asyncio.get_event_loop_policy().get_event_loop does not. Similarly,
        # none of the set_event_loop methods warn, although comments on
        # https://bugs.python.org/issue39529 indicate that they are also
        # intended for future removal.
        #
        # Therefore, we first attempt to access the event loop with the
        # (non-warning) policy method, and if it fails, fall back to creating a
        # new event loop. We do not have effective test coverage of the
        # new event loop case; this will have to be watched when/if
        # get_event_loop is actually removed.
        self.should_close_asyncio_loop = False
        try:
            self.asyncio_loop = asyncio.get_event_loop_policy().get_event_loop()
        except Exception:
            self.asyncio_loop = asyncio.new_event_loop()
            self.should_close_asyncio_loop = True

        async def get_loop() -> IOLoop:
            return self.get_new_ioloop()

        self.io_loop = self.asyncio_loop.run_until_complete(get_loop())
        with warnings.catch_warnings():
            warnings.simplefilter("ignore", DeprecationWarning)
            self.io_loop.make_current()

    def tearDown(self) -> None:
        # Native coroutines tend to produce warnings if they're not