code: def test_is_tournament():
      G = DiGraph()
      G.add_edges_from([(0, 1), (1, 2), (2, 3), (3, 0), (1, 3), (0, 2)])
      assert is_tournament(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 3 for calling a global function with example usage: test_is_tournament() without return types