code: def test_no_backtracking():
      N = 5
      G = dgl.from_networkx(nx.star_graph(N))
      L = G.line_graph(backtracking=False)
      assert L.num_nodes() == 2 * N
      for i in range(1, N):
          e1 = G.edge_ids(0, i)
          e2 = G.edge_ids(i, 0)
          assert not L.has_edges_between(e1, e2)
          assert not L.has_edges_between(e2, e1)
  
imports: import math
  import os
  import unittest
  import backend
  import dgl
  import dgl.function
  import dgl.partition
  import networkx
  import numpy
  import pytest
  from scipy import sparse
  from utils import parametrize_idtype
  from utils.graph_cases import get_cases
label_desc: Use image node_id 6 for calling a global function with example usage: test_no_backtracking() without return types