Oracle 12C -- clone a non-cdb as a pdb

$ sqlplus '/as sysdba'
SQL> select name, decode(cdb, 'YES', 'Multitenant Option enabled', 'Regular 12c Database: ') "Multitenant Option" , open_mode, con_id from v$database;

NAME      Multitenant Option         OPEN_MODE                CON_ID
--------- -------------------------- -------------------- ----------
TEST      Regular 12c Database:      READ WRITE                    0

SQL> shutdown immediate;
SQL> startup open read only;

$ sqlplus '/as sysdba'
SQL> select name, decode(cdb, 'YES', 'Multitenant Option enabled', 'Regular 12c Database: ') "Multitenant Option" , open_mode, con_id from v$database;

NAME      Multitenant Option         OPEN_MODE                CON_ID
--------- -------------------------- -------------------- ----------
ORA12     Multitenant Option enabled READ WRITE                    0

SQL> create database link link_test connect to system identified by oracle using 'test';

SQL> create pluggable database pdb_test from NON$CDB@link_test create_file_test='/u12/app/oracle/oradata/pdb_test';
SQL> alter session set container=pdb_test;
SQL> @$ORACLE_HOME/rdbms/admin/noncdb_to_pdb;

SQL> alter pluggable database pdb_test open;