class_docstr: Unit tests for the
  :func:`~networkx.algorithms.matching.maximal_matching`.
code: def test_self_loops(self):
      # Create the path graph with two self-loops.
      G = nx.path_graph(3)
      G.add_edges_from([(0, 0), (1, 1)])
      matching = nx.maximal_matching(G)
      assert len(matching) == 1
      # The matching should never include self-loops.
      assert not any(u == v for u, v in matching)
      assert nx.is_maximal_matching(G, matching)
  
imports: import math
  from itertools import permutations
  from pytest import raises
  import networkx
  from networkx.algorithms.matching import matching_dict_to_set
  from networkx.utils import edges_equal
label_desc: Use image node_id 3 for calling the TestMaximalMatching obj's underlying member method code with example usage: obj.test_self_loops() without return types