Unit Testing with ActiveRecord External Database Tables

I want to perform unit tests but the model object in question is
actually linked to an external database table. So I don't actually have
the database table in my local database which I need to run unit tests.
Any ideas on how to approach this? I have created a sample fixtures yml
file that has a subset of data from my external database table I'd like
to use.

My setup:

I have a rake task that populates a schema based on a predefined legacy
table. I connect to that table via:

class ExternalDBEvent < ActiveRecord::Base
establish_connection :external_db
set_table_name :event

I have connection parameters defined in database.yml