anchor.diff:  
   t_1_test() ->
     Filename = "redbug.txt",
  -  {_, _} = redbug:start("lists:sort->return", [{print_file, Filename}]),
  +  {_,_} = redbug:start("lists:sort->return",[{print_file,Filename},buffered]),
     [1,2,3] = lists:sort([3,2,1]),
     timer:sleep(100),
     redbug:stop(),
  
positive.code: stack() ->
    stack(self()).
  stack(P) ->
    [string:strip(e(2,(string:tokens(L,"(+)")))) || L<- bt(P), $0 =:= hd(L)].
  bt(P) ->
    string:tokens(binary_to_list(e(2,(process_info(P,backtrace)))),"\n").
  
  
negative.code: 
  t_01_test() ->
    Filename = "redbug.txt",
    {_,_} = redbug:start("lists:sort",[{print_file,Filename},arity]),
    [1,2,3] = lists:sort([3,2,1]),
    timer:sleep(100),
    redbug:stop(),
  