[Oracle] ORA-65096: 無效的通用使用者或角色名稱

Problem
As I tried to create a new user, I got the following error:

SQL> CREATE USER test_user IDENTIFIED BY oracle;    
CREATE USER test_user IDENTIFIED BY oracle          
            *                                       
 ERROR 在行 1:                                        
ORA-65096: 無效的通用使用者或角色名稱                            
                                                  

How-To

SQL> alter session set "_ORACLE_SCRIPT"=true;       
已更改階段作業.                                            
                                                    
                                                    
SQL> CREATE USER test_user IDENTIFIED BY oracle;    
已建立使用者.             

Reference
[1] https://stackoverflow.com/a/41490385/6314840