Mocha expectation on association build call failing

Question

I have this example:

# GET New
context "on get to new" do
  it "should assign cardset" do
    @profile.cardsets.expects(:build).once.returns(Factory.stub(:cardset))
    get :new
    assigns[:cardset].should_not be_nil
  end
end

To test this method:

# GET /cardsets/new
def new
  @cardset = current_user.cardsets.build
end

I am trying to enforce that the association is built from current_user to make sure the user is only creating things that belong to themselves. I am using an expectation very similarly to ensure they are calling find from the current_user object and it works find, but when running the above example I get:

6)
Mocha::ExpectationError in 'CardsetsController for a logged in user on get to new should assign cardset'
not all expectations were satisfied
unsatisfied expectations:
- expected exactly once, not yet invoked: [#<Cardset:0x102eaa8c8>, #<Cardset:0x102e12438>].build(any_parameters)
satisfied expectations:
- allowed any number of times, not yet invoked: ApplicationController.require_user(any_parameters)
- allowed any number of times, already invoked twice: #<CardsetsController:0x1030849c8>.current_user(any_parameters)

/Applications/MAMP/htdocs/my_app/spec/controllers/cardsets_controller_spec.rb:32: