rails unit testing removes foreign key constraints in test database?

I've noticed that when testing is finished that at some point Rails
has removed the foreign key constraints from my test database. Does
anyone know where this foreign key constraint deletion occurs in the
source code. I'd like to turn it off.

Thanks,
Peter

After much hunting, I found the issue. I needed to add the following
to my environment.rb file

  config.active_record.schema_format = :sql

Peter