Authority Check

Hi

I have coded in my program abt the authority check on a particular field of selection screen..

what i want is to test it..what shud i do or how shud i test whether the authority check is functioning properly or not...i tried changing the user name sy-user in debug mode by using some user name..but it is displaying the report output..

i want to do some testing where i want to see an error message that iam not authorised to see the output..

what shud i do??

Tahnks

Shakir