def remove(self, elem):
        """Remove a requirement.

        :param elem: a string or :class:`Requirement` instance.
        """
        if isinstance(elem, text_type):
            for requirement in self:
                if requirement.package == elem:
                    return super(Requirements, self).remove(requirement)
        return super(Requirements, self).remove(elem)
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,
        )