Installing R-2.15.2 in Debian Wheezy/Testing

["Stephen P. Molnar" <s.molnar@sbcglobal.net>]

The current version of R that is available in Wheezy is 2.15.1. However, 
version 2.15.2 is available at CRAN sites.  The site I use is 
http://cran.case.edu/bin/linux/debian which states:

'If you want to have up to date R on wheezy I propose to directly 
install Dirks packages from unstable (sid) by creating a file 
/etc/apt/preferences containing
   Package: *
   Pin: release a=testing
   Pin-Priority: 650

   Package: *
   Pin: release a=unstable
   Pin-Priority: 600

and adding a line for unstable in /etc/apt/sources.list.'

I assume that the preference file should be in /etc/apt and not in 
/etc/apt/preferences.d

My question is what should be the format of the line in the sources.lists?

Thanks in advance