ruby on rails - Rspec should_receive has me stumped -

i need test whether instance method gets called on particular instance result of calling class method. like:

class dog < activerecord::base   def self.roll_trained     dog.all.each { |d| d.rollover if d.trained? }   end    def rollover     # rollover , stuff   end   def trained?     self.trained == true   end end 

i've written test like:

describe 'dog.roll_trained'   'rolls trained dogs'     dog_1 = dog.create(trained: true)     dog_1.should_receive(:rollover)     dog.roll_trained   end end 

i thought had right, test fails. doing wrong here?

the problem here dog_1 , instances looped on dog.each not same instance. because activerecord generates different instance same row (dog_1) in database when dog.each

i have written blog post on can read here: activerecord , in-memory object state

one solution stub dog.all - dog.stub(all: [dog_1])

another solution save trained attribute database , spec against database: dog_1.reload.trained.should be_true