group writable file not writable [duplicate]

Question

Possible Duplicate:
Linux Group Permissions

I have a file with following permissions

$ ls -l setup.txt
-rwxrwxr-x 1 www-data www-data 10741 2011-10-12 14:15 setup.txt

I belong to www-data group

$ groups `whoami`
auniyal : auniyal adm dialout cdrom audio www-data plugdev lpadmin admin sambashare vboxusers

So I was thinking I should be able to write to that file but I am not

$ test -w setup.txt && echo "Writable" || echo "Not Writable"
Not Writable

so how is it determined that file is writable or not, because my thinking was if file is group writable and I belong to that group I should be able to write to that file?

and in case it helps directory is also group writable

$ ls -l ..
...
drwxrwxr-x 10 www-data www-data    4096 2011-12-07 09:42 timesite
...

Answer 1

I needed to log-out and log-in again as I just added myself to www-data group

Linux Group Permissions