code: def test_digraph2(self):
      # An example in which some edges end up with zero flow.
      G = nx.DiGraph()
      G.add_edge("s", "b", capacity=2)
      G.add_edge("s", "c", capacity=1)
      G.add_edge("c", "d", capacity=1)
      G.add_edge("d", "a", capacity=1)
      G.add_edge("b", "a", capacity=2)
      G.add_edge("a", "t", capacity=2)
  
      H = {
          "s": {"b": 2, "c": 0},
          "c": {"d": 0},
          "d": {"a": 0},
          "b": {"a": 2},
          "a": {"t": 2},
          "t": {},
      }
  
      compare_flows_and_cuts(G, "s", "t", H, 2)
  
imports: import pytest
  import networkx
  from networkx.algorithms.flow import boykov_kolmogorov, build_flow_dict, build_residual_network, dinitz, edmonds_karp, preflow_push, shortest_augmenting_path
label_desc: Use image node_id 4 for calling the TestMaxflowMinCutCommon obj's underlying member method code with example usage: obj.test_digraph2() without return types