anchor.diff:  %%%----------------------------------------------------------------
  +%%%
   %%% File        : btree_tests.erl
   %%% Author      : Mikael Pettersson <mikael.pettersson@klarna.com>
   %%% Description : Tests for Erlang implementation of B-tree sets
   %%%
  -%%% Copyright (c) 2016 Klarna AB
  +%%% Copyright (c) 2016-2017 Klarna AB
   %%%
   %%% This file is provided to you under the Apache License,
   %%% Version 2.0 (the "License"); you may not use this file
  
positive.code: %%% KIND, either express or implied.  See the License for the
  %%% specific language governing permissions and limitations
  %%% under the License.
  %%%----------------------------------------------------------------
  
  -module(btree_tests).
  
negative.code: %% Exercise an order-2 B-tree using a sequence of insertions and deletions
  %% taken from [Wirth76].
  wirth_test() ->
    Keys = wirth_keys(),
    {ETS, IO} = io_init(),
    Btree1 = insert_all(IO, btree:new(2), Keys),
    Btree2 = delete_all(IO, Btree1, lists:reverse(Keys)),
    ?assertEqual([], btree:all_keys(IO, Btree2)),
    io_fini(ETS).
  
  wirth_keys() ->
    [20, 40, 10, 30, 15, 35, 7, 26, 18, 22, 5, 42, 13, 46, 27, 8, 32,
     38, 24, 45, 25].
  
  insert_all(IO, Btree, Keys) ->
    lists:foldl(fun (Key, Btree1) -> insert_one(IO, Btree1, Key) end,
  