code: def test_asia_graph_dsep(asia_graph):
      """Example-based test of d-separation for asia_graph."""
      assert nx.is_d_separator(
          asia_graph,
          {"asia", "smoking"},
          {"dyspnea", "xray"},
          {"bronchitis", "either"},
      )
      assert nx.is_d_separator(
          asia_graph,
          {"tuberculosis", "cancer"},
          {"bronchitis"},
          {"smoking", "xray"},
      )
  
imports: from itertools import combinations
  import pytest
  import networkx
label_desc: Use image node_id 21 for calling a global function with example usage: test_asia_graph_dsep(asia_graph) without return types