text: import json
  from nose.tools import assert_equal, assert_true, raises
  import cynetworkx as nx
  from cynetworkx.readwrite.json_graph import *
  
  
  class TestTree:
  
      def test_graph(self):
          G = nx.DiGraph()
          G.add_nodes_from([1, 2, 3], color='red')
          G.add_edge(1, 2, foo=7)
          G.add_edge(1, 3, foo=10)
          G.add_edge(3, 4, foo=10)
          H = tree_graph(tree_data(G, 1))
          nx.is_isomorphic(G, H)
  
      def test_graph_attributes(self):
          G = nx.DiGraph()
          G.add_nodes_from([1, 2, 3], color='red')
          G.add_edge(1, 2, foo=7)
          G.add_edge(1, 3, foo=10)
          G.add_edge(3, 4, foo=10)
          H = tree_graph(tree_data(G, 1))
          assert_equal(H.nodes[1]['color'], 'red')
  
          d = json.dumps(tree_data(G, 1))
          H = tree_graph(json.loads(d))
          assert_equal(H.nodes[1]['color'], 'red')
  
      @raises(nx.NetworkXError)
      def test_exception(self):
          G = nx.MultiDiGraph()
          G.add_node(0)
          attrs = dict(id='node', children='node')
          tree_data(G, 0, attrs)
  