stubbing CAPTCHA to pass Cucumber scenario

Hi, I'm trying to start using cucumber. I've done login, logout scenarious, but stumbled in CAPTCHA validation on user registration page. As I get I should stub CAPTCHA validation method. I guess I should implement stubbing Given step or include stubbing code in Before filter?

I use validates_captcha gem, thus instance method to stub is

module ValidatesCaptcha   module ModelValidation     module InstanceMethods       private       def validate_captcha         # doing nothing means passing       end     end   end end

I've read these posts http://vinsol.com/blog/2006/07/21/rails-captcha-and-testing-using-mock-objects/ http://www.brynary.com/2009/2/3/cucumber-step-definition-tip-stubbing-time but still don't get where should I put stubbing code, should I call stub! method and if so, of which object?