code: def test_markov_condition(graph):
      """Test that the Markov condition holds for each PGM graph."""
      for node in graph.nodes:
          parents = set(graph.predecessors(node))
          non_descendants = (
              graph.nodes
              - nx.descendants(graph, node)
              - {node}
              - parents
          )
          assert nx.is_d_separator(
              graph, {node}, non_descendants, parents
          )
  
imports: from itertools import combinations
  import pytest
  import networkx
label_desc: Use image node_id 16 for calling a global function with example usage: test_markov_condition(graph) without return types