Can I test Extended Query in core test framework

I want to write some test cases with extended query in core test system.
basically it looks like

PreparedStatement preparedStatement = conn.prepareStatement("select *
from bigtable");
preparedStatement.setFetchSize(4);
ResultSet rs = preparedStatement.executeQuery();
while(rs.next())
{
System.out.println(rs.getInt(1));
// conn.commit();
conn.rollback();
}

However I don't find a way to do that after checking the example in
src/test/xxx/t/xxx.pl
where most often used object is PostgresNode, which don't have such
abilities.

Can I do that in core system, I tried grep '\->prepare' and '\->execute'
and get nothing.
am I miss something?

--
Best Regards
Andy Fan