public void testFactory_parseDays_String() {
        assertEquals(0, Days.parseDays((String) null).getDays());
        assertEquals(0, Days.parseDays("P0D").getDays());
        assertEquals(1, Days.parseDays("P1D").getDays());
        assertEquals(-3, Days.parseDays("P-3D").getDays());
        assertEquals(2, Days.parseDays("P0Y0M2D").getDays());
        assertEquals(2, Days.parseDays("P2DT0H0M").getDays());
        try {
            Days.parseDays("P1Y1D");
            fail();
        } catch (IllegalArgumentException ex) {
            // expeceted
        }
        try {
            Days.parseDays("P1DT1H");
            fail();
        } catch (IllegalArgumentException ex) {
            // expeceted
        }
    }