[Rspec-users] how to spec elements of config file usage

[Pauli's List Subscriptions]

Hi!

I'm pretty newbie in Ruby and certainly in rspec.  

I'm writing a wrapper to a 3rd party API in Ruby, and
will use a config file to persist the API user keys. 
In setting up my specs I want to say things like:

"should raise exception if config file not found"
"should raise exception if config file does not
contain key"

I figure that I'll swap config files in the beginning
of each spec.

If I 'require rake' in my spec script, I'll be able to
use the File methods from rake to swap out versions of
my config file - right?  Any reason not to do it that
way, i.e. some other Ruby library is better?

Other recommended methods to handle specs around
presence / contents of file system objects?

Thanks,

Pauli