assertTrue( constraint.isValid( null, null ), "null fails validation." );
// Test allowed zone offsets (UTC-18 to UTC+18) with 1 hour increments
for ( int i = -18; i <= 18; i++ ) {
ZoneId zone = ZoneId.ofOffset( "UTC", ZoneOffset.ofHours( i ) );
ChronoZonedDateTime future = ZonedDateTime.now( zone ).plusHours( 1 );
ChronoZonedDateTime past = ZonedDateTime.now( zone ).minusHours( 1 );
assertTrue( constraint.isValid( future, null ), "Future ZonedDateTime '" + future + "' fails validation." );
assertFalse( constraint.isValid( past, null ), "Past ZonedDateTime '" + past + "' validated as future." );
}
}