code: def test_weighted_all_zero(self):
      edges = pd.DataFrame(
          {"source": [0, 0], "target": [1, 2], "weight": [0.0, 0]}
      )
  
      g = StellarDiGraph(edges=edges)
      bfw = DirectedBreadthFirstNeighbours(g)
      walks = bfw.run(
          nodes=[0],
          n=10,
          in_size=[20, 20],
          out_size=[20, 20],
          weighted=True,
      )
  
      assert len(walks) == 10
      for walk in walks:
          assert len(walk) == 7
          assert walk[0] == [0]
          for hop in walk:
              np.testing.assert_array_equal(hop[1:], -1)
  
file_path: stellargraph/tests/data/test_directed_breadth_first_sampler.py
imports: import random
  import pytest
  import pandas
  import numpy
  from stellargraph.data.explorer import DirectedBreadthFirstNeighbours
  from stellargraph.core.graph import StellarDiGraph
  from ..test_utils.graphs import create_test_graph, tree_graph, example_graph_random, weighted_tree
label_desc: Use image node_id 8 for calling the TestDirectedBreadthFirstNeighbours obj's underlying member method code with example usage: obj.test_weighted_all_zero() without return types