Hi Carol,
The Test as a User ability should appear when you are signed into an App you are an admin in when you click on your name where it appears in the upper right hand corner of an application.
If it isn't showing up in that dropdown any longer I would suggest taking a look at your role in the application and make sure that Test as User hasn't been hidden under the User Interface options in your role. I would also check in with your Account Admin to see if they possibly disabled it for your Account. I hope this information is helpful Carol.
