Use specific RAILS_ENV for a single unit test

I have a specific test I'd like to write to check for regressions. I've inherited a Rails environment that had no unit tests and there have been very few guards against what is put into the database via external (outside of Rails) means.

The unit test would iterate over a specific model in the database and render a view, ensuring that every instance could still be rendered correctly in that view. I'd like to run this against a development database instance which is usually a clone of the production database (mysql).

The data is too large to put into fixtures... I'd like to keep the rest of the tests using the 'test' sqlite database.

So - is there a way to override for a single test which database Rails is connected to?

I'm using Rails 3.2.22.