assertTrue("Expected another permutation, but there was none.", permutations.hasNext());
    assertEquals(expectedPermutation, permutations.next());
  }

  private <T> void assertNoMorePermutations(Iterator<List<T>> permutations) {
    assertFalse("Expected no more permutations, but there was one.", permutations.hasNext());
    try {
      permutations.next();
      fail("Expected NoSuchElementException.");

    assertTrue("Expected another permutation, but there was none.", permutations.hasNext());
    assertEquals(expectedPermutation, permutations.next());
  }

  private <T> void assertNoMorePermutations(Iterator<List<T>> permutations) {
    assertFalse("Expected no more permutations, but there was one.", permutations.hasNext());
    try {
      permutations.next();
      fail("Expected NoSuchElementException.");