def test_source_array(self):
     self.assertIsNone(get_common_node(self.edges, [], "A"),
                       "Should be empty")
 def test_dest_array(self):
     self.assertIsNone(get_common_node(self.edges, "A", []),
                       "Should be empty")
 def test_all_none(self):
     self.assertIsNone(get_common_node(None, None, None), "Should be empty")
 def test_empty_edge_array(self):
     self.assertIsNone(get_common_node([], "I", "A"), "Should be empty")
 def test_with_undirected_input(self):
     self.assertEqual(get_common_node(self.edges, 'I', 'B'), 'E',
                      "Should be in center")
 def test_with_valid_input(self):
     self.assertEqual(get_common_node(self.edges, 'A', 'B'), 'E',
                      "Should be in center")