def METHOD_NAME(self) -> Deferred[None]:
    """
    The checker created by the C{--auth} command-line option returns a
    L{Deferred} that returns the avatar id when presented with credentials
    that are known to that checker.
    """
    self.options.parseOptions(["--auth", "file:" + self.filename])
    checker: ICredentialsChecker = self.options["credCheckers"][-1]
    correct = UsernamePassword(*self.usernamePassword)
    d = checker.requestAvatarId(correct)
    def checkSuccess(username: Union[bytes, Tuple[()]]) -> None:
        self.assertEqual(username, correct.username)
    return d.addCallback(checkSuccess)