RSpec mocking of existing methods in Ruby?!?

Foo.rb

class Foo
  def bar(n)
    return gin n
  end

  def gin(n)
    return n+1
  end
end
 

Foo_spec.rb

require 'Foo'

describe "Foo, bar"
  it "uses gin" do
    Foo.new.stub!(:gin).and_return(1)
    Foo.new.bar(3).should == 1
  end
end

Try this:

describe "Foo, bar" do
  it "uses gin" do
    foo = Foo.new
    foo.stub!(:gin).and_return(1)
    foo.bar(3).should == 1
  end
end

Hint: you don't need the return in the methods of Foo.

Explanation: in Foo_spec.rb#5 you create an instance and prepare the stub. In #6 you instanciate another Foo that does not know anything about the stub declared above. Huh? Thus the .should == 1 fails.

Thanks indeed for your guidance.

As a beginner it was not obvious to me that i'd mock out an instance of the method of that class rather than the definition of the method of that class. Good to know. BTW, it worked out well, just finished my first ruby code kata:
https://github.com/ilkerde/CodeKatas/tree/master/KataFizzBuzz.RSpec ;-)