@Override
    public Position position(int major, int minor) {
        return new Pos(major, minor);
    }
@Test
    public void testZeroOffsetWithBackwardBias() {
        Position pos = navigator.position(3, 0);
        pos = pos.offsetBy(0, Backward);
        assertEquals(2, pos.getMajor());
        assertEquals(10, pos.getMinor());

        // additional zero backward offset should have no effect
        assertEquals(pos, pos.offsetBy(0, Backward));
    }