postgresql function execution taking too long

Below is my Postgres funtion

CREATE OR REPLACE FUNCTION public.test_me(test_id _int4) RETURNS TEXT AS $BODY$ DECLARE tempIds INT[]; returnValue TEXT := 'Success'; BEGIN RAISE NOTICE ' selecting abc_id for : %', test_id; tempIds := ARRAY ( SELECT DISTINCT abc_id FROM test WHERE test_id IN ( SELECT unnest(test_id)) ); RAISE NOTICE ' selected abc_id are : %', tempIds; RETURN returnValue; END; $BODY$ LANGUAGE plpgsql VOLATILE; 

and I am executing it like this

select test_me('{123}'::int[]); 

It takes forever to run and I observed that only the first notice is printed during the execution and it never reaches to the second notice statement. when I run the select query inside ARRAY method it executes quickly.

Edit 1: When I tried running the select query like this

SELECT DISTINCT abc_id FROM test WHERE test_id IN (123) 

it executed very fast as test_id is an indexed column.

But when I tried it like this

SELECT DISTINCT abc_id FROM test WHERE test_id IN ( SELECT unnest('{123}'::int[]) 

It took lot of time since due to unnest inside IN clause query was using a sequential scan on test_id column and taking a lot of time to run.

So the main culprit is the unnest inside IN clause.

Any substitute to use an array inside an in clause with indexed search?