How to test inside a controller test that a model receives a message

def charge
  authorize(@order)
  stripe_token = params.require :stripe_token
  if @order.charge! stripe_token
    flash[:success] = t '.success'
    redirect_to my_reservations_orders_path
  else
    @order.reload # for cleaning up any possibly modified attributes
    flash[:error] = t 'stripe.payment_failed'
    redirect_to @order.payment_link
  end
end

def set_order
  @order = SpaceOrder.find_by(id: params[:order_id])
end

describe '#charge!' do
  ...
  let(:stripe_token) { SecureRandom.hex }
  let(:order_params) {
    {
      id: order.space_id,
      order_id: order.id,
      stripe_token: stripe_token
    }
  }
  def the_action
    post :charge, order_params
  end
        
  ...
  
  describe "paying an open order I own" do
    let(:space)            { FactoryGirl.create :space, :fixed_price, billable_type, :approved }
    let(:order)             { FactoryGirl.create type, billable_type, :approved, user: user, space: space }
      it "invokes Order#charge!", :aggregate_failures do
        ensure_order_is_payable_and_user_owns_it(order, user)
        # next line is necessary because the instance that is receiving the message 'charge!' is the new one created in the controller, not the creating in the test
        expect(SpaceOrder).to receive(:find_by).with(id: order.id.to_s).and_return(order)
        expect(order).to receive(:charge!).and_call_original
        the_action
      end