Ruby on rails 正在验证同一属性测试的存在性和内容类型

这是我的RubyonRails模型

 class Item < ApplicationRecord
  has_attached_file :image,
    :styles => { :medium => "400x400>", :thumb => "100x100>", :square =>       "300x300#" }, default_url: "/images/:style/missing.png"
  validates_presence_of(:description, :color, :category, :size, :image)
  validates_attachment_content_type :image, :content_type => /\Aimage\/.*\Z/
  belongs_to :user
end 

根据自述文件，您可以使用单个验证程序语句进行多个验证。大概是这样的：

class Item < ApplicationRecord
  has_attached_file :image,
    :styles => { :medium => "400x400>", :thumb => "100x100>", :square =>       "300x300#" }, default_url: "/images/:style/missing.png"

  validates_presence_of(:description, :color, :category, :size)
  validates_attachment :image,
    content_type: { :content_type => /\Aimage\/.*\Z/ }
    presence: true

  belongs_to :user
end

---

我想出来了。结果很简单

it "is not valid without an image" do
  expect{item[:image] = nil}.to raise_error(NameError)
end

---

仍然不知道如何测试它

it "is not valid without an image" do
  expect{item[:image] = nil}.to raise_error(NameError)
end