Rails ActiveRecord依赖注入非db属性

Question

我有一个带有私有方法的ActiveRecord模型，该方法进行外部HTTP调用。该方法由面向公众的方法调用。出于测试目的，我想存根发出请求的HTTP客户端，因此希望能够注入HTTP客户端并将其设置为ActiveRecord类的属性。我怎样才能做到这一点？或者是否有更好的方法来实现我想要实现的目标？

我想要实现的目标：

# in my models:

class Model < ActiveRecord::Base
  def public_facing_method
    ...
    res = make_external_call
    ...
  end      

  private
    def make_external_call
      @client.post(...)  # client is injected on init (HTTParty in my case)
    end
end

# in my tests:

class ModelTest < ActiveSupport::TestCase
  test "Model#public_facing_method should work"
    stub_client = MyStubHTTPClient
    # is below possible? + would it work in all cases? (ie: when fetching from db)
    instance = Model.new(..., stub_client)  
    instance.public_facing_method
    ...
  end
end

也许我采取了错误的做法。任何建议都将非常感谢！