How does Index Scan get used

I tried an Index Scan but I kept on getting Seq Scan. Do you know why ? What do I need to do to get my query to use index scan (I tried to turn it on by doing SET ENABLE_indexscan = on; but it didn't work)

create table test (test_col text);
create index test_index on test (test_col);
insert into test values ('abc.xyz');
insert into test values ('abcxyz');
insert into test values ('abc/xyz');

explain select * from test where test_col like 'abc/%';

NOTICE: QUERY PLAN:

Seq Scan on test (cost=0.00..22.50 rows=10 width=12)

Another question:
Does Regex (~*) or like use table scan ?

Thanks,
Sam
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