text: """
      Tests for VF2 isomorphism algorithm.
  """
  
  import os
  import struct
  import random
  
  from nose.tools import assert_true, assert_equal
  import networkx as nx
  from networkx.algorithms import isomorphism as iso
  
  class TestWikipediaExample(object):
      # Source: http://en.wikipedia.org/wiki/Graph_isomorphism
  
      # Nodes 'a', 'b', 'c' and 'd' form a column.
      # Nodes 'g', 'h', 'i' and 'j' form a column.
      g1edges = [['a','g'], ['a','h'], ['a','i'], 
                 ['b','g'], ['b','h'], ['b','j'], 
                 ['c','g'], ['c','i'], ['c','j'], 
                 ['d','h'], ['d','i'], ['d','j']]
  
      # Nodes 1,2,3,4 form the clockwise corners of a large square.
      # Nodes 5,6,7,8 form the clockwise corners of a small square 
      g2edges = [[1,2], [2,3], [3,4], [4,1], 
                 [5,6], [6,7], [7,8], [8,5], 
                 [1,5], [2,6], [3,7], [4,8]]
  
      def test_graph(self):
          g1 = nx.Graph()
          g2 = nx.Graph()
          g1.add_edges_from(self.g1edges)
          g2.add_edges_from(self.g2edges)
          gm = iso.GraphMatcher(g1,g2)
          assert_true(gm.is_isomorphic())
  
          mapping = sorted(gm.mapping.items())
  # this mapping is only one of the possibilies 
  # so this test needs to be reconsidered 
  #        isomap = [('a', 1), ('b', 6), ('c', 3), ('d', 8), 
  #                  ('g', 2), ('h', 5), ('i', 4), ('j', 7)]
  #        assert_equal(mapping, isomap)
          
      def test_subgraph(self):
          g1 = nx.Graph()
          g2 = nx.Graph()
          g1.add_edges_from(self.g1edges)
          g2.add_edges_from(self.g2edges)
          g3 = g2.subgraph([1,2,3,4])
          gm = iso.GraphMatcher(g1,g3)
          assert_true(gm.subgraph_is_isomorphic())
  
  class TestVF2GraphDB(object):
      # http://amalfi.dis.unina.it/graph/db/
  
      @staticmethod
      def create_graph(filename):
          """Creates a Graph instance from the filename."""
  
          # The file is assumed to be in the format from the VF2 graph database.
          # Each file is composed of 16-bit numbers (unsigned short int).
          # So we will want to read 2 bytes at a time.
  
          # We can read the number as follows:
          #   number = struct.unpack('<H', file.read(2))
          # This says, expect the data in little-endian encoding
          # as an unsigned short int and unpack 2 bytes from the file.
  
          fh = open(filename, mode='rb')
  
          # Grab the number of nodes.
          # Node numeration is 0-based, so the first node has index 0.
          nodes = struct.unpack('<H', fh.read(2))[0]
  
          graph = nx.Graph()
          for from_node in range(nodes):
              # Get the number of edges.
              edges = struct.unpack('<H', fh.read(2))[0]
              for edge in range(edges):
                  # Get the terminal node.
                  to_node = struct.unpack('<H', fh.read(2))[0]
                  graph.add_edge(from_node, to_node)
  
          fh.close()
          return graph
  
      def test_graph(self):
          head,tail = os.path.split(__file__)
          g1 = self.create_graph(os.path.join(head,'iso_r01_s80.A99'))
          g2 = self.create_graph(os.path.join(head,'iso_r01_s80.B99'))
          gm = iso.GraphMatcher(g1,g2)
          assert_true(gm.is_isomorphic())
  
      def test_subgraph(self):
          # A is the subgraph
          # B is the full graph
          head,tail = os.path.split(__file__)
          subgraph = self.create_graph(os.path.join(head,'si2_b06_m200.A99'))
          graph = self.create_graph(os.path.join(head,'si2_b06_m200.B99'))
          gm = iso.GraphMatcher(graph, subgraph)
          assert_true(gm.subgraph_is_isomorphic())
  
  def test_graph_atlas():
      #Atlas = nx.graph_atlas_g()[0:208] # 208, 6 nodes or less
      Atlas = nx.graph_atlas_g()[0:100]
      alphabet = list(range(26))
      for graph in Atlas:
          nlist = graph.nodes()
          labels = alphabet[:len(nlist)]
          for s in range(10):
              random.shuffle(labels)
              d = dict(zip(nlist,labels))
              relabel = nx.relabel_nodes(graph, d)
              gm = iso.GraphMatcher(graph, relabel)
              assert_true(gm.is_isomorphic())
  
  def test_multiedge():
      # Simple test for multigraphs
      # Need something much more rigorous
      edges = [(0, 1), (1, 2), (2, 3), (3, 4), (4, 5), 
               (5, 6), (6, 7), (7, 8), (8, 9), (9, 10), 
               (10, 11), (10, 11), (11, 12), (11, 12), 
               (12, 13), (12, 13), (13, 14), (13, 14), 
               (14, 15), (14, 15), (15, 16), (15, 16), 
               (16, 17), (16, 17), (17, 18), (17, 18), 
               (18, 19), (18, 19), (19, 0), (19, 0)]
      nodes = list(range(20))
  
      for g1 in [nx.MultiGraph(), nx.MultiDiGraph()]:
          g1.add_edges_from(edges)
          for _ in range(10):
              new_nodes = list(nodes)
              random.shuffle(new_nodes)
              d = dict(zip(nodes, new_nodes))
              g2 = nx.relabel_nodes(g1, d)
              if not g1.is_directed():
                  gm = iso.GraphMatcher(g1,g2)
              else:
                  gm = iso.DiGraphMatcher(g1,g2)
              assert_true(gm.is_isomorphic())
  
  def test_selfloop():
      # Simple test for graphs with selfloops
      edges = [(0, 1), (0, 2), (1, 2), (1, 3), (2, 2), 
               (2, 4), (3, 1), (3, 2), (4, 2), (4, 5), (5, 4)]
      nodes = list(range(6))
  
      for g1 in [nx.Graph(), nx.DiGraph()]:
          g1.add_edges_from(edges)
          for _ in range(100):
              new_nodes = list(nodes)
              random.shuffle(new_nodes)
              d = dict(zip(nodes, new_nodes))
              g2 = nx.relabel_nodes(g1, d)
              if not g1.is_directed():
                  gm = iso.GraphMatcher(g1,g2)
              else:
                  gm = iso.DiGraphMatcher(g1,g2)
              assert_true(gm.is_isomorphic())
  
  def test_isomorphism_iter1():
      # As described in:
      # http://groups.google.com/group/networkx-discuss/browse_thread/thread/2ff65c67f5e3b99f/d674544ebea359bb?fwc=1
      g1 = nx.DiGraph()
      g2 = nx.DiGraph()
      g3 = nx.DiGraph()
      g1.add_edge('A','B')
      g1.add_edge('B','C')
      g2.add_edge('Y','Z')
      g3.add_edge('Z','Y')
      gm12 = iso.DiGraphMatcher(g1,g2)
      gm13 = iso.DiGraphMatcher(g1,g3)
      x = list(gm12.subgraph_isomorphisms_iter())
      y = list(gm13.subgraph_isomorphisms_iter())
      assert_true({'A':'Y','B':'Z'} in x)
      assert_true({'B':'Y','C':'Z'} in x)
      assert_true({'A':'Z','B':'Y'} in y)
      assert_true({'B':'Z','C':'Y'} in y)
      assert_equal(len(x),len(y))
      assert_equal(len(x),2)
  
  def test_isomorphism_iter2():
      # Path
      for L in range(2,10):
          g1 = nx.path_graph(L)
          gm = iso.GraphMatcher(g1,g1)
          s = len(list(gm.isomorphisms_iter()))
          assert_equal(s,2)
      # Cycle
      for L in range(3,10):
          g1 = nx.cycle_graph(L)
          gm = iso.GraphMatcher(g1,g1)
          s = len(list(gm.isomorphisms_iter()))
          assert_equal(s, 2*L)
  
  def test_multiple():
      # Verify that we can use the graph matcher multiple times
      edges = [('A','B'),('B','A'),('B','C')]
      for g1,g2 in [(nx.Graph(),nx.Graph()), (nx.DiGraph(),nx.DiGraph())]:
          g1.add_edges_from(edges)
          g2.add_edges_from(edges)
          g3 = nx.subgraph(g2, ['A','B'])
          if not g1.is_directed():
              gmA = iso.GraphMatcher(g1,g2)
              gmB = iso.GraphMatcher(g1,g3)
          else:
              gmA = iso.DiGraphMatcher(g1,g2)
              gmB = iso.DiGraphMatcher(g1,g3)
          assert_true(gmA.is_isomorphic())
          g2.remove_node('C')
          assert_true(gmA.subgraph_is_isomorphic())
          assert_true(gmB.subgraph_is_isomorphic())
  #        for m in [gmB.mapping, gmB.mapping]:
  #            assert_true(m['A'] == 'A')
  #            assert_true(m['B'] == 'B')
  #            assert_true('C' not in m)
  
  