Here is the mysterious: I have a scope which looks like this (in Image.rb) scope :moderate_all, delegates.where("moderation_flag = #{$moderation_flags[:not_moderated]}") Note that delegates is another scope that I am defining before moderate_all When I leave it like this, I can run my test that checks if an image has been "checked-out" it is not available anymore. I don't put the code of the test, because it does not matter actually. With this code, when I run "rake test" it fails, but if I do "ruby test/unit/image_test.rb" it works! I was thinking I am starting to have a bad day. Then I tried scope :moderate_all, lambda { delegates.where("moderation_flag = #{$moderation_flags[:not_moderated]}") } And "rake test" passes! So my problem is solved, but why?