new_contents: from nose.tools import *
  import networkx as nx
  
  
  class TestReciprocity(object):
  
      # test overall reicprocity by passing whole graph
      def test_reciprocity_digraph(self):
          DG = nx.DiGraph([(1, 2), (2, 1)])
          reciprocity = nx.reciprocity(DG)
          assert reciprocity == 1.0
  
      # test empty graph's overall reciprocity which will throw an error
      @raises(nx.NetworkXError)
      def test_overall_reciprocity_empty_graph(self):
          DG = nx.DiGraph()
          nx.overall_reciprocity(DG)
  
      # test for reciprocity for a list of nodes
      def test_reciprocity_graph_nodes(self):
          DG = nx.DiGraph([(1, 2), (2, 3), (3, 2)])
          reciprocity = nx.reciprocity(DG, [1, 2])
          expected_reciprocity = {1: 0.0, 2: 0.6666666666666666}
          assert reciprocity == expected_reciprocity
  
      # test for reciprocity for a single node
      def test_reciprocity_graph_node(self):
          DG = nx.DiGraph([(1, 2), (2, 3), (3, 2)])
          reciprocity = nx.reciprocity(DG, 2)
          assert reciprocity == 0.6666666666666666
  
      # test for reciprocity for an isolated node
      @raises(nx.NetworkXError)
      def test_reciprocity_graph_isolated_nodes(self):
          DG = nx.DiGraph([(1, 2)])
          DG.add_node(4)
          nx.reciprocity(DG, 4)
  
subject: add tests for networkx.algorithms.reciprocity