How write rspec test for state_machine transition callback

Question

I have spree Adjustment extension

Spree::Adjustment.class_eval do
  state_machine do
    after_transition :to => :closed, :do => :some_method
  end
  def some_method
  end
end

And I have rspec test, which fails. In real application method are called and all things work as expected.

describe Spree:Adjustment do 
    let(:adjustment) { create(:adjustment, state: 'open') }
    it "call some_method after close" do
      adjustment.should_receive(:some_method)
      adjustment.state = "closed"
    end
end    

failed with

 1) Spree::Adjustment call some_method after close
 Failure/Error: adjustment.should_receive(:some_method)
   (#<Spree::Adjustment:0x0000000751a340>).some_method(any args)
       expected: 1 time with any arguments
       received: 0 times with any arguments

Answer 1

State machine transition don't work if you set state explicitly, like you do, with Adjustment#state= method (in this case). You should use events instead, for example:

adjustment.close