@Test
 public void testCombinationSum4() throws Exception {
   assertEquals("[]", combinationSum.combinationSum(new int[] {3, 3, 3}, 1).toString());
 }
 @Test
 public void testCombinationSum2() throws Exception {
   assertEquals(
       "[[2, 2, 3], [7]]", combinationSum.combinationSum(new int[] {3, 6, 2, 7}, 7).toString());
 }
 @Test
 public void testCombinationSum3() throws Exception {
   assertEquals("[[1, 1, 1]]", combinationSum.combinationSum(new int[] {1}, 3).toString());
 }
 @Test
 public void testCombinationSum1() throws Exception {
   assertEquals(null, combinationSum.combinationSum(new int[] {}, 7));
   assertEquals(null, combinationSum.combinationSum(null, 7));
 }