Re: [PATCH] Improve amcheck to also check UNIQUE constraint in btree index.

The pstrdup is unnecessary but harmless.

> - use the existing table for uniqueness check in 005_opclass_damage.pl

It appears you still create a new table, bttest_unique, rather than using the existing table int4tbl.  That's fine.

> - added tests into 003_check.pl . It is only smoke test that just verifies new functions.

You have borrowed the existing tests but forgot to change their names.  (The last line of each check is the test name, such as 'pg_amcheck smoke test --parent-check'.)  Please make each test name unique.