how to found a variable is in a aggregation or not?

I want to check a variable is in a aggregattion or not, so I create a
function as below:

create or replace function anytest(val text) returns boolean as $$
begin
perform 1 where quote_literal(val) in ('hello', 'world', 'test');
if not found then
return false;
else
return true;
end if;
end;
$$ language plpgsql;

but when I used, I got the result below, why?

test=# select anytest('world111');
anytest
---------
f
(1 row)

test=# select anytest('world');
anytest
---------
f
(1 row)

any help is appreciated.

regards,
Zy