Ruby on rails 如何在RSpec中编写可重用的共享示例

每次运行此操作时，我总是得到一个

错误数量的参数（1代表0）

。我做错了什么

describe Payment do
  before  { @payment = build_stubbed(:payment) }
  subject { @payment }

  shared_examples 'a foreign key' do |key|
    it "can't be nil, blank, or not an int" do
      [nil, "", " ", "a", 1.1].each do |value|
        @payment.send key, value
        @payment.should_not be_valid
      end
    end
  end

  describe "validation" do
    describe "order_id" do
      it_behaves_like 'a foreign key', :order_id
    end
  end
end

失败消息：

1) Payment validation order_id behaves like a foreign key can't be nil, blank, or not an int
     Failure/Error: @payment.send(key, value)
     ArgumentError:
       wrong number of arguments (1 for 0)
     Shared Example Group: "a foreign key" called from ./spec/models/payment_spec.rb:27
     # ./spec/models/payment_spec.rb:18:in `block (4 levels) in <top (required)>'
     # ./spec/models/payment_spec.rb:17:in `each'
     # ./spec/models/payment_spec.rb:17:in `block (3 levels) in <top (required)>'

1）支付验证顺序\u id的行为与外键的行为类似，外键不能为零、空或非整数
失败/错误：@payment.send（键，值）
参数错误：
参数数目错误（1代表0）
共享示例组：./spec/models/payment_spec.rb:27调用的“外键”
#./spec/models/payment_spec.rb:18:in'block（4层）in'
#/规格/型号/付款规格rb:17:“每个”
#./spec/models/payment_spec.rb:17:in'block（3层）in'

我没有正确提供setter方法：

@payment.send（key，value）

相反，我需要使用

@payment.send（“#{key}=”，value）