You can only be logged in to one account at a time, so to log in to your test account you've got to log out of your boot account.
That's not quite correct. If you have fast user switching enabled (via
System Preferences ->
Accounts ->
Login Options), you can log in to another account without logging out of the account you started in.
You'll have to authenticate to get back in to that account, and some applications or processes which can only function in one account at a time will be suspended until your return, but generally speaking, all applications and documents you had open will stay open in your absence.
