@Test
void testGetRollUpPermutationsAsPositionsTagCountTwo() {

    final Set<List<Integer>> perms = RollUpBitMask.getRollUpPermutationsAsPositions(2);
    assertThat(perms.size()).isEqualTo(4);
    assertThat(perms.contains(Collections.<Integer>emptyList())).isTrue();
    assertThat(perms.contains(Arrays.asList(1))).isTrue();
    assertThat(perms.contains(Arrays.asList(0))).isTrue();
    assertThat(perms.contains(Arrays.asList(0, 1))).isTrue();
}