def METHOD_NAME(self):
    path = tests.get_data_path(
        ("NetCDF", "unstructured_grid", "theta_nodal_xios.nc")
    )
    self.src = iris.load_cube(path, "Potential Temperature")
    src_lat = self.src.coord("latitude")
    src_lon = self.src.coord("longitude")
    src_lat.coord_system = src_lon.coord_system = GeogCS(6370000)
    src_lat.convert_units(Unit("degrees"))
    src_lon.convert_units(Unit("degrees"))
    self.global_grid = global_pp()