text: import json
  from nose.tools import assert_equal, assert_true, raises
  import networkx as nx
  from networkx.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)
  