def recruit(spy)
      raise AlreadyStubbedError if @spies[spy.object_id]
      check_spy!(spy)
      @spies[spy.object_id] = spy
    end
def recruit(spy)
      raise AlreadyStubbedError if @spies[spy.object_id]
      check_spy!(spy)
      @spies[spy.object_id] = spy
    end
Record that a spy was initialized and hooked
 @param spy [Subroutine, Constant, Double]
 @return [spy]