运行应该测试时，遇到nMethod：NilClass时遇到NoMethodError：未定义的方法'class_name'

Question

我在Rails中使用这个MiniTest遇到了问题。

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输出：

#device_test.rb
require 'test_helper'
  should have_one(:vendor).through(:hardware)
end

根据我从多个来源收集的信息

• https://github.com/thoughtbot/shoulda-matchers/issues/646
• https://github.com/Casecommons/pg_search/issues/120
• Shoulda Matcher and has_many through: undefined method `class_name' for nil:NilClass

我的问题是我没有正确建立直通关系，但是从我的收集中看来这是正确的。

Error:
DeviceTest#test_: Device should have one vendor through hardware. :
NoMethodError: undefined method `class_name' for nil:NilClass

然后它导致认为拐点存在问题，但是我在控制台中签到，并且我相信#models/device.rb class Device < ApplicationRecord belongs_to :site belongs_to :hardware has_one :vendor, through: :hardware end #models/hardware.rb class Hardware < ApplicationRecord has_many :devices belongs_to :vendor end #models/vendor.rb class Vendor < ApplicationRecord has_many :hardwares has_many :devices, through: :hardwares end ，hardware和device具有正确的复数形式。

非常感谢您提供任何纠正此错误的帮助。