def load(self, requirements_file=None):
        """Load or reload requirements from a requirements.txt file.

        :param requirements_file: if not given, the filename used from
            initialization will be read again.
        """
        if requirements_file is None:
            requirements_file = self.filename
            if requirements_file is None:
                raise ValueError("no filename provided")
        elif isinstance(requirements_file, text_type):
            requirements_file = Path(requirements_file)
        self.clear()
        with requirements_file.open() as f:
            self.loads(f.read())

        if isinstance(requirements_file, (text_type, Path)):
            self.filename = requirements_file
def test_config_errors(self):
        Session = scoped_session(sa.orm.sessionmaker())

        s = Session()  # noqa
        assert_raises_message(
            sa.exc.InvalidRequestError,
            "Scoped session is already present",
            Session,
            bind=testing.db,
        )

        assert_warns_message(
            sa.exc.SAWarning,
            "At least one scoped session is already present. ",
            Session.configure,
            bind=testing.db,
        )