-- test some errors
CREATE EXTENSION test_ext1;
ERROR:  required extension "test_ext2" is not installed
HINT:  Use CREATE EXTENSION CASCADE to install required extensions too.
CREATE EXTENSION test_ext1 SCHEMA test_ext1;
ERROR:  schema "test_ext1" does not exist
CREATE EXTENSION test_ext1 SCHEMA test_ext;
ERROR:  schema "test_ext" does not exist
CREATE SCHEMA test_ext;
CREATE EXTENSION test_ext1 SCHEMA test_ext;
ERROR:  extension "test_ext1" must be installed in schema "test_ext1"
-- finally success
CREATE EXTENSION test_ext1 SCHEMA test_ext CASCADE;
NOTICE:  installing required extension "test_ext2"
NOTICE:  installing required extension "test_ext3"
NOTICE:  installing required extension "test_ext5"
NOTICE:  installing required extension "test_ext4"
SELECT extname, nspname, extversion, extrelocatable FROM pg_extension e, pg_namespace n WHERE extname LIKE 'test_ext%' AND e.extnamespace = n.oid ORDER BY 1;
  extname  |  nspname  | extversion | extrelocatable 
-----------+-----------+------------+----------------
 test_ext1 | test_ext1 | 1.0        | f
 test_ext2 | test_ext  | 1.0        | t
 test_ext3 | test_ext  | 1.0        | t
 test_ext4 | test_ext  | 1.0        | t
 test_ext5 | test_ext  | 1.0        | t
(5 rows)

CREATE EXTENSION test_ext_cyclic1 CASCADE;
NOTICE:  installing required extension "test_ext_cyclic2"
ERROR:  cyclic dependency detected between extensions "test_ext_cyclic1" and "test_ext_cyclic2"
DROP SCHEMA test_ext CASCADE;
NOTICE:  drop cascades to 5 other objects
DETAIL:  drop cascades to extension test_ext3
drop cascades to extension test_ext5
drop cascades to extension test_ext2
drop cascades to extension test_ext4
drop cascades to extension test_ext1