Unit test using sql file

Hi,

I am using Rails3 with postgreSQL and my database has some additional
constraints which cannot be included in schema.rb.

To run unit test, I have found that I have to enable the following
option:
config.active_record.schema_format = :sql
so that rails can setup the database correctly with additional
constraints.

I could dump development_structure.sql and test_structure.sql but
when I run “rake test:units”, rails still reads schema.rb to prepare
the database.

Does anyone know how to change rails behavior to read sql dump files?

My environment is:
Fedora 14
Ruby 1.9.2p180
Rails 3.0.9
Postgresql 8.4.8-1