解决方法
看看
http://blog.ardes.com/2006/12/11/testing-singletons-with-ruby：
require 'singleton'
class <<Singleton
def included_with_reset(klass)
included_without_reset(klass)
class <<klass
def reset_instance
Singleton.send :__init__,self
self
end
end
end
alias_method :included_without_reset,:included
alias_method :included,:included_with_reset
end