@Test
public void testSplit_OneZero() {

    // split((i, 0)) = ((i1,0), (i2,0)), where (i1, i2) = split(i)
    ID[] splitOne = one.split();
    ID[] expected = new ID[] {
        IDs.with(splitOne[0], zero),
        IDs.with(splitOne[1], zero)
    };
    assertArrayEquals(expected, oneZero.split());
}