Rake test task looks at wrong database

I'm new to contributing to Rails, but want to help by contributing.

I've started off with a simple ticket:

http://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/1599-rake-test-task-looks-at-wrong-database

Can someone please see if I've misunderstood how it works.

Also, the contributor guide is great, but I'm not 100% sure how to use
my locally checked out copy of rails to generate a new project to test
it with (I made the same change using monkey patching in a Rakefile
and it worked). Can someone let me know how to do that.

Thanks,

Andy