code: def test_k_factor4(self):
      g = gen.lattice.hexagonal_lattice_graph(4, 4)
      # Perfect matching doesn't exist for 4,4 hexagonal lattice graph
      with pytest.raises(nx.NetworkXUnfeasible):
          reg.k_factor(g, 2)
  
imports: import pytest
  import networkx
  import networkx
  import networkx.algorithms.regular
  import networkx.generators
label_desc: Use image node_id 5 for calling the TestKFactor obj's underlying member method code with example usage: obj.test_k_factor4() without return types