code: def test_cyclic_graphs_raise_error():
      """
      Test that cycle graphs should cause erroring.
  
      This is because PGMs assume a directed acyclic graph.
      """
      g = nx.cycle_graph(3, nx.DiGraph)
      with pytest.raises(nx.NetworkXError):
          nx.is_d_separator(g, {0}, {1}, {2})
      with pytest.raises(nx.NetworkXError):
          nx.find_minimal_d_separator(g, {0}, {1})
      with pytest.raises(nx.NetworkXError):
          nx.is_minimal_d_separator(g, {0}, {1}, {2})
  
imports: from itertools import combinations
  import pytest
  import networkx
label_desc: Use image node_id 23 for calling a global function with example usage: test_cyclic_graphs_raise_error() without return types