code: def testMaxFlowValue(self):
      self.assertTrue(self.g.maxflow_value(0, 3) == 2)
      self.assertTrue(self.g.maxflow_value(0, 3, self.capacities) == 4)
      self.assertTrue(self.g.maxflow_value(0, 3, "capacity") == 4)
      self.assertRaises(KeyError, self.g.maxflow_value, 0, 3, "unknown")
  
imports: import unittest
  from igraph import Cut, Graph, EdgeSeq, InternalError
  from itertools import combinations
  from random import randint
label_desc: Use image node_id 5 for calling the MaxFlowTests obj's underlying member method code with example usage: obj.testMaxFlowValue() without return types