Hi!
I would make two cosmetic changes.
1. I suggest replace description of function bt_report_duplicate() from
```
/*
  * Prepare and print an error message for unique constrain violation in
  * a btree index under WARNING level. Also set a flag to report ERROR
  * at the end of the check.
  */
```
to
```
/*
  * Prepare an error message for unique constrain violation in
  * a btree index and report ERROR.
  */
```
2. I think will be better to change test 004_verify_nbtree_unique.pl - 
replace
```
use Test::More tests => 6;
```
to
```
use Test::More;
...
done_testing();
```
(same as in the other three tests).
-- 
With best regards,
Dmitry Koval
Postgres Professional: http://postgrespro.com