def add_test(self, test, system_name):
        if self._callable_dict.has_key(system_name):
            raise ValueError(system_name % "test for '%s' already present.")
        if system_name == 'UNKNOWN':
            raise ValueError("Invalid system name")
        assert isinstance(system_name, str)
        self._callable_dict[system_name] = test
dataset/ETHPy150Open VisTrails/VisTrails/vistrails/gui/bundles/utils.py/System_guesser.add_test/swapped operands of `%`