public void testFormat_invalid() {
        try {
            DateTimeFormat.forPattern(null);
            fail();
        } catch (IllegalArgumentException ex) {}
        try {
            DateTimeFormat.forPattern("");
            fail();
        } catch (IllegalArgumentException ex) {}
        try {
            DateTimeFormat.forPattern("A");
            fail();
        } catch (IllegalArgumentException ex) {}
        try {
            DateTimeFormat.forPattern("dd/mm/AA");
            fail();
        } catch (IllegalArgumentException ex) {}
    }