Ruby on rails 轨道4+；Rspec+；Carrierwave：Carrierwave期望属性是哪个类的实例？

这是我使用CarrierWave的模型：

class UploadedPrescription < ActiveRecord::Base
  mount_uploader :file, FileUploader  
  belongs_to :order

  validates_presence_of :file
end

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你有没有试着传递一个文件。打开（路径到文件）？是的，谢谢

u = UploadedPrescription.new(file: ??what do i put here??)