How to use the cjio.models.CityObject function in cjio

def test_build_index(self, lod):
        co = models.CityObject(id='one')
        geom = models.Geometry(type='Solid', lod=lod)
        co.geometry.append(geom)
        geometry, vtx_lookup, vtx_idx = co.build_index()
        assert 'semantics' not in geometry[0]

parents = co['parents'] if 'parents' in co else None
        attributes = co['attributes'] if 'attributes' in co else None
        # cast to objects
        geometry = []
        for geom in co['geometry']:
            semantics = geom['semantics'] if 'semantics' in geom else None
            geometry.append(
                models.Geometry(
                    type=geom['type'],
                    lod=geom['lod'],
                    boundaries=geom['boundaries'],
                    semantics_obj=semantics,
                    vertices=rotterdam_subset.j['vertices']
                )
            )
        rotterdam_subset.cityobjects[co_id] = models.CityObject(
            id=id,
            type=co['type'],
            attributes=attributes,
            children=children,
            parents=parents,
            geometry=geometry
        )
    yield rotterdam_subset

parents = co['parents'] if 'parents' in co else None
        attributes = co['attributes'] if 'attributes' in co else None
        # cast to objects
        geometry = []
        for geom in co['geometry']:
            semantics = geom['semantics'] if 'semantics' in geom else None
            geometry.append(
                models.Geometry(
                    type=geom['type'],
                    lod=geom['lod'],
                    boundaries=geom['boundaries'],
                    semantics_obj=semantics,
                    vertices=rotterdam_subset.j['vertices']
                )
            )
        rotterdam_subset.cityobjects[co_id] = models.CityObject(
            id=id,
            type=co['type'],
            attributes=attributes,
            children=children,
            parents=parents,
            geometry=geometry
        )
    yield rotterdam_subset

parents = co['parents'] if 'parents' in co else None
        attributes = co['attributes'] if 'attributes' in co else None
        # cast to objects
        geometry = []
        for geom in co['geometry']:
            semantics = geom['semantics'] if 'semantics' in geom else None
            geometry.append(
                models.Geometry(
                    type=geom['type'],
                    lod=geom['lod'],
                    boundaries=geom['boundaries'],
                    semantics_obj=semantics,
                    vertices=zurich_subset.j['vertices']
                )
            )
        zurich_subset.cityobjects[co_id] = models.CityObject(
            id=co_id,
            type=co['type'],
            attributes=attributes,
            children=children,
            parents=parents,
            geometry=geometry
        )
    return zurich_subset