看一下你对应的测试代码是不是 user 和 user1 只调用过一个。

Note that let is lazy-evaluated: it is not evaluated until the first time the method it defines is invoked.

关于 let 和 let!: https://www.relishapp.com/rspec/rspec-core/v/3-3/docs/helper-methods/let-and-let

git commit -m "Update a" 细心点啊。。

Object.class # => Class
Class.superclass.superclass # => Object

ruby-style-guide rails-style-guide

可以用

begin
  puts val
  val += 1
end while val < 0

但是推荐用

loop do
  puts val
  val += 1
  break unless val < 0
end

参见ruby-style-guide

关于Array#slice an empty array is returned when the starting index for an element range is at the end of the array. Returns nil if the index (or starting index) are out of range. 来源 ruby-doc

http://stackoverflow.com/questions/5183975/factory-girl-whats-the-purpose 也许可以看看这里面的回答。