Tests failing on table with primary key as string

Hi,
I’ve got a table where the primary key named :id is a string.
Everything works great using the app however when I try to write a test
I notice that rails keeps converting this id into a Fixnum, which
results in it querying the database for ids that don’t exist. Is there
anyway I can get my tests to work?

For example, I have a fixture with
ABook:
id: “123456789X”
title: “Title of my book”

then in my test if I print out books(:ABook).id.class I get a FixNum.

I’m using edge Rails by the way.

Thanks,
Ray