code: def test_weighted_all_zero(self):
      edges = pd.DataFrame(
          {"source": [0, 0], "target": [1, 2], "weight": [0.0, 0]}
      )
  
      g = StellarGraph(edges=edges)
      bfw = SampledBreadthFirstWalk(g)
      walks = bfw.run(nodes=[0], n=10, n_size=[20, 20], weighted=True)
  
      assert len(walks) == 10
      for walk in walks:
          assert len(walk) == 1 + 20 + 20 * 20
          assert walk[0] == 0
          np.testing.assert_array_equal(walk[1:], -1)
  
file_path: stellargraph/tests/data/test_breadth_first_walker.py
imports: import pandas
  import pytest
  import numpy
  from stellargraph.data.explorer import SampledBreadthFirstWalk
  from stellargraph.core.graph import StellarGraph, StellarDiGraph
  from ..test_utils.graphs import create_test_graph, tree_graph, example_graph_random, weighted_tree
label_desc: Use image node_id 11 for calling the TestBreadthFirstWalk obj's underlying member method code with example usage: obj.test_weighted_all_zero() without return types