Tests fail through rake

I have a strange problem. I have three controllers of same name
EntitiesController. One is under rest/entities_controller.rb and is
called Rest::EntitiesController, the other is under admin/
entities_controller.rb in module Admin::EntitiesController and the
last one is in app/controllers/entities_controller.rb and is called
When I execute tests separately, All is fine but when I do this:

rake test:functionals

Then the tests of app/controllers/entities_controller.rb fail. On
investigation, it revealed that the tests of this controller are
posting there requests to actually rest/entities_controller.rb.
I thougth doing this
require "#{RAILS_ROOT}/app/controllers/entities_controller.rb"

at the top of test/functional/entities_controller.rb would fix the
problem but no gain.

What might be the problem? Please guide me in this regard.