code: def test_naive_bayes_dsep(naive_bayes_graph):
      """Example-based test of d-separation for naive_bayes_graph."""
      for u, v in combinations(range(1, 5), 2):
          assert nx.is_d_separator(naive_bayes_graph, {u}, {v}, {0})
          assert not nx.is_d_separator(
              naive_bayes_graph, {u}, {v}, set()
          )
  
imports: from itertools import combinations
  import pytest
  import networkx
label_desc: Use image node_id 20 for calling a global function with example usage: test_naive_bayes_dsep(naive_bayes_graph) without return types