code: def test_attribute_mixing_dict_multigraph(self):
      d = nx.attribute_mixing_dict(self.M, "fish")
      d_result = {"one": {"one": 4}, "two": {"two": 2}}
      assert d == d_result
  
imports: import pytest
  import networkx
  from .base_test import BaseTestAttributeMixing, BaseTestDegreeMixing
label_desc: Use image node_id 3 for calling the TestAttributeMixingDict obj's underlying member method code with example usage: obj.test_attribute_mixing_dict_multigraph() without return types