@Test
 public void testConstruction() {
   UndirectedGraph abc = new UndirectedGraph();
   assertEquals(0, abc.size());
   assertTrue(abc.isEmpty());
   assertEquals(Arrays.asList(), abc.getNodes());
 }
 @Test
 public void testCombined() {
   UndirectedGraphNode a = new UndirectedGraphNode("A");
   UndirectedGraphNode b = new UndirectedGraphNode("B");
   UndirectedGraphNode c = new UndirectedGraphNode("C");
   test.addNode(a);
   assertEquals(1, test.size());
   test.addNode(b);
   assertEquals(2, test.size());
   test.addNode(c);
   assertEquals(3, test.size());
   assertEquals(Arrays.asList(a, b, c), test.getNodes());
   test.removeNode(a);
   //		System.out.println(test.getNodes());
   assertEquals(2, test.size());
   test.removeNode(b);
   //		System.out.println(test.getNodes());
   assertEquals(1, test.size());
   test.removeNode(c);
   //		System.out.println(test.getNodes());
   assertEquals(0, test.size());
   assertTrue(test.isEmpty());
 }