code: def test_fork_graph_dsep(fork_graph):
      """Example-based test of d-separation for fork_graph."""
      assert nx.is_d_separator(fork_graph, {1}, {2}, {0})
      assert not nx.is_d_separator(fork_graph, {1}, {2}, set())
  
imports: from itertools import combinations
  import pytest
  import networkx
label_desc: Use image node_id 18 for calling a global function with example usage: test_fork_graph_dsep(fork_graph) without return types