def test_is_iterable(self, inp):
        snap = make_1d_traj([0.0])[0]
        volume = self._vol_for_cv_type(inp)
        val = volume.collectivevariable(snap)
        expected = inp in ['array', 'array1']
        if expected:
            with pytest.warns(UserWarning, match="returns an iterable"):
                result = volume._is_iterable(val)
        else:
            result = volume._is_iterable(val)

        assert result is expected