ruby on rails - Testing association methods with Mocha -

i have rails app order , refund model. order has_many :refunds. , good. i'm trying write functional test refund logic in controller. here's have right now:

test "should not process partial paypal refund partially refunded order when refund total plus refund amount greater order total"     set_super_admin_login_credentials     o = order.new     o.stubs({:id => 1234567, :source => "paypal", :total => 39.95, :user => users(:dave)})     order.stubs(:find).with(1234567).returns(o)     :refund, {:order_id => 1234567}     assert_equal o, assigns(:order)     o.refunds.build.stubs({:amount => 1.0})     o.refunds.build.stubs({:amount => 30.00})     assert_raise         post :refund, {:order_id => 1234567, :refund_amount => 10.00}     end end 

and in controller, refund method looks this:

def refund         @order = order.find(params[:order_id])     return if request.get?      amount = params[:refund_amount].to_f     raise "cannot refund order more total" if (@order.refunds.sum(&:amount) + amount)     # refund stuff end 

some notes:

1. i'm basing o.refunds.build bit on ryan bates' railscast. if not right or no longer relevant, that's helpful information.

2. i've seen lot of conflicting information how sum method, & , without. in script/console, & blows without it, actual sum. in controller, however, if switch &:amount :amount, message: nomethoderror: undefined method+' :amount:symbol`

i feel there's conceptual information missing rather bug somewhere, i'll appreciate pointers.

finally figured out issue. stubbing empty association [] rather leaving nil rails handle on other methods. so, when change one, other fail. word wise: enumerable#sum , activerecord::associations::associationcollection#sum take entirely different parameters. :)

so, changing stubs leave off :refunds => [] , using string field name in sum got things normal. so, here's functional version of above code:

test "should not process partial paypal refund partially refunded order when refund total plus refund amount greater order total"     set_super_admin_login_credentials     o = order.new     o.stubs({:id => 1234567, :source => "paypal", :total => 39.95, :user => users(:dave)})     order.stubs(:find).with(1234567).returns(o)     :refund, {:order_id => 1234567}     assert_equal o, assigns(:order)     o.refunds.build.stubs({:amount => 1.0})     o.refunds.build.stubs({:amount => 30.00})     assert_raise         post :refund, {:order_id => 1234567, :refund_amount => 10.00}     end end  def refund         @order = order.find(params[:order_id])     return if request.get?      amount = params[:refund_amount].to_f     raise "cannot refund order more total" if (@order.refunds.sum('amount') + amount)     # refund stuff end