In this file: https://github.com/mongoid/mongoid/blob/master/lib/mongoid/railtie.rb#L2, mongoid is required, and,
in this file: https://github.com/mongoid/mongoid/blob/master/lib/mongoid.rb#L30, railtie is required which gives the following warning while running rspecs:

ruby-2.1.0/gems/mongoid-4.0.0/lib/mongoid/railtie.rb:2: warning: loading in progress, circular require considered harmful - ..../.rvm/gems/ruby-2.1.0/gems/mongoid-4.0.0/lib/mongoid.rb