A.K.A, it’s difficult to change the DNS point in hosts file with OS X based system, you never can get right to save with default text editor, and VIM with sudo is terrible for tester. :(
This solution is not simple but does work.
####Sublime Text 2
Sublime is a wonderful text editor on Mac OS X, it’s not free but you can use it with license alert sometimes.
Download and Install from HERE.
####Open Hosts file
File > Open to show open file window.
/etc folder is for system and hidden, Hit
Command+Shift+G to show go to folder option and input the hosts file path manually like below:
Then it will locate to the hosts file and open it.
####Save changes to disk
Command + S to save (or click save on menu)
System will show a popup let you input password to authorization, only need at the first time in one session.
Hope it helps someone.