code: def test_same_node_is_reachable():
      """Tests that a node is always reachable from it."""
      # G is an arbitrary tournament on ten nodes.
      G = DiGraph(sorted(p) for p in combinations(range(10), 2))
      assert all(is_reachable(G, v, v) for v in G)
  
imports: from itertools import combinations
  import pytest
  from networkx import DiGraph
  from networkx.algorithms.tournament import hamiltonian_path, index_satisfying, is_reachable, is_strongly_connected, is_tournament, random_tournament, score_sequence, tournament_matrix
label_desc: Use image node_id 18 for calling a global function with example usage: test_same_node_is_reachable() without return types