create or replace 
function is_output_enabled return boolean deterministic is
   str_long constant varchar(32767):=rpad('x',32767);
begin
   dbms_output.new_line;
   dbms_output.put(str_long);
   dbms_output.put(str_long);
   return false;
exception 
   when others then 
      return true; 
end;
/

SQL> set serverout on size 10000
SQL> begin
  2     dbms_output.put_line('old data');
  3     if is_output_enabled
  4        then dbms_output.put_line('enabled');
  5        else raise_application_error(-20000,'disabled');
  6     end if;
  7  end;
  8  /
old data
enabled

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.01
SQL> set serverout off
SQL> begin
  2     dbms_output.put_line('old data');
  3     if is_output_enabled
  4        then dbms_output.put_line('enabled');
  5        else raise_application_error(-20000,'disabled');
  6     end if;
  7  end;
  8  /
begin
*
ERROR at line 1:
ORA-20000: disabled
ORA-06512: at line 5


Elapsed: 00:00:00.01
SQL> declare
  2     function is_output_enabled return boolean deterministic is
  3        str_long constant varchar(32767):=rpad('x',32767);
  4     begin
  5        dbms_output.new_line;
  6        dbms_output.put(str_long);
  7        dbms_output.put(str_long);
  8        return false;
  9     exception
 10        when others then
 11           return true;
 12     end;
 13  begin
 14     dbms_output.put_line('old data');
 15     if is_output_enabled
 16        then dbms_output.put_line('enabled');
 17        else raise_application_error(-20000,'disabled');
 18     end if;
 19  end;
 20  /
declare
*
ERROR at line 1:
ORA-20000: disabled
ORA-06512: at line 17


Elapsed: 00:00:03.08

SQL> select * from v$version;

BANNER                                                                               CON_ID
-------------------------------------------------------------------------------- ----------
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production              0
PL/SQL Release 12.2.0.1.0 - Production                                                    0
CORE    12.2.0.1.0      Production                                                                0
TNS for Linux: Version 12.2.0.1.0 - Production                                            0
NLSRTL Version 12.2.0.1.0 - Production                                                    0

Elapsed: 00:00:00.30

SQL> @plans/flush_sql.sql
Enter value for sql_id: c8wpgq87py4ax

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.19
SQL> @tests/output
declare
*
ERROR at line 1:
ORA-20000: disabled
ORA-06512: at line 17


Elapsed: 00:00:03.13
SQL> @tests/output
declare
*
ERROR at line 1:
ORA-20000: disabled
ORA-06512: at line 17


Elapsed: 00:00:00.29
SQL> @plans/flush_sql.sql
Enter value for sql_id: c8wpgq87py4ax

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.14
SQL> @tests/output
declare
*
ERROR at line 1:
ORA-20000: disabled
ORA-06512: at line 17


Elapsed: 00:00:03.17