public void testParseMutablePeriod_simple() {
        MutablePeriod expect = new MutablePeriod(1, 2, 3, 4, 5, 6, 7, 8);
        assertEquals(expect, f.parseMutablePeriod("P1Y2M3W4DT5H6M7.008S"));
        
        try {
            f.parseMutablePeriod("ABC");
            fail();
        } catch (IllegalArgumentException ex) {}
    }