SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (GLOBAL_DBNAME = orcl12c)
      (SID_NAME = orcl12c)
      (ORACLE_HOME = /u01/app/oracle/product/12.2/db_1)
    )
    (SID_DESC =
      (GLOBAL_DBNAME = testDB)
      (SID_NAME = testDB)
      (ORACLE_HOME = /u01/app/oracle/product/12.2/db_1)
    )
    (SID_DESC =
      (GLOBAL_DBNAME = TESTCDB)
      (SID_NAME = TESTCDB)
      (ORACLE_HOME = /u01/app/oracle/product/12.2/db_1)
    )
    (SID_DESC =
      (GLOBAL_DBNAME = standby_test)
      (SID_NAME = standby_test)
      (ORACLE_HOME = /u01/app/oracle/product/12.2/db_1)
    )
  )

[oracle@localhost admin]$ lsnrctl start standby_test

LSNRCTL for Linux: Version 12.2.0.1.0 - Production on 27-APR-2019 13:42:35

Copyright (c) 1991, 2016, Oracle.  All rights reserved.

Starting /u01/app/oracle/product/12.2/db_1/bin/tnslsnr: please wait...


TNSLSNR for Linux: Version 12.2.0.1.0 - Production
System parameter file is /u01/app/oracle/product/12.2/db_1/network/admin/listener.ora
Log messages written to /u01/app/oracle/diag/tnslsnr/localhost/standby_test/alert/log.xml
TNS-01151: Missing listener name, standby_test, in LISTENER.ORA

Listener failed to start. See the error message(s) above...