@Test
void requirement() {

    assertSame(SpigotMapper.TRUE, mapper.requirement(Literal.of("a").requires(null).build()));
    
    Predicate<CommandSender> predicate = mock(Predicate.class);
    mapper.requirement(Literal.of("a").requires(predicate).build()).test(listener);
    
    verify(predicate).test(sender);
}