undefined method `post' and 'assign'

I have an error of undefined method.
can anyone help me to solve it.
I follow the tutorial to practicing testing controller of rails, and
now i got stuck with the error.. plz help

error:
undefined method `post' for
#<Spec::Example::ExampleGroup::Subclass_1:0xb7754114>
undefined method `assigns' for
#<Spec::Example::ExampleGroup::Subclass_1:0xb785d1b4>

Test file

describe "GET Index" do
def mock_product(stubs={})
post 'index'
@mock_user ||= mock_model(User, stubs).as_null_object
end

def setup
   @user = User.new
end

controller file

def index
    @users = User.find(:all)
     end

please give me some help ..

thanks
Yennie