Unit testing models for legacy tables


I have an application that needs to access legacy tables that are in a
different database then the Rails application. I know how to set up the
models to connect to the legacy tables and that seems to work just fine.
I would like to do unit testing on these models using Rails built in
testing. I haven’t found anything that explains how to get the schemas
for the legacy tables into a test environment. I don’t have migrations
for them and they aren’t in schema.db. What do I need to do to set this