code: def testCombinationDefaultOverride(self):
      g = self.g
      g.simplify(combine_edges={None: "max", "weight": "sum"})
      self.assertTrue(g.es["weight"] == [3, 3, 15])
      self.assertTrue(g.es["weight2"] == [2, 3, 6])
  
imports: import unittest
  from igraph import Graph
label_desc: Use image node_id 16 for calling the AttributeCombinationTests obj's underlying member method code with example usage: obj.testCombinationDefaultOverride() without return types