code: def test_mean_zero_degree(g, idtype):
      g = g.astype(idtype).to(F.ctx())
      g.ndata["h"] = F.ones((g.num_nodes(), 3))
      g.update_all(fn.copy_u("h", "m"), fn.mean("m", "x"))
      deg = F.asnumpy(g.in_degrees())
      v = F.tensor(np.where(deg == 0)[0])
      assert F.allclose(
          F.gather_row(g.ndata["x"], v), F.zeros((len(v), 3))
      )
  
file_path: dgl/tests/python/common/test_heterograph-kernel.py
imports: from itertools import product
  import backend
  import dgl
  import dgl.function
  import networkx
  import numpy
  import pytest
  from utils import get_cases, parametrize_idtype
label_desc: Use image node_id 10 for calling a global function with example usage: test_mean_zero_degree(g, idtype) without return types