integer column to serial "type"

Hello,
there is some way to get and old integer primary key column to show the "type"
serial at table description?

I had a table like this:

CREATE TABLE test
(
test_id integer NOT NULL,
CONSTRAINT test_pkey PRIMARY KEY (test_id),
);

that i would like to see as:

CREATE TABLE test
(
test_id serial NOT NULL,
CONSTRAINT test_pkey PRIMARY KEY (test_id),
);

i have tried with:

CREATE SEQUENCE test_test_id_seq;
ALTER TABLE test ALTER COLUMN test_id SET DEFAULT
nextval('test_test_id_seq'::regclass);
ALTER SEQUENCE test_test_id_seq OWNED BY test.test_id;

and now i have this table:

CREATE TABLE test
(
test_id integer NOT NULL DEFAULT nextval('test_test_id_seq'::regclass),
CONSTRAINT test_pkey PRIMARY KEY (test_id),
);

i know this works the same as serial but do i have some way to get this table to
show me test_id column as "serial" type without have to recreate the table and
restore original rows?

Regards,
Miguel Angel.