anchor.diff:                                end, Values),
       Result = lists:map(fun(Value) -> {Value, 1} end, SortedValues),
       ?equals(histogram_rt:get_data(H2), Result),
  -    ok.
  +    true.
   
  -merge_keys(_Config) ->
  +add_keys(_Config) ->
  +    tester:test(?MODULE, prop_add_keys, 3, 250, [{threads, 2}]).
  +
  +-spec prop_merge_keys(BaseKey::?RT:key(), Key1::?RT:key(), Key2::?RT:key()) -> true.
  +prop_merge_keys(BaseKey, Key1, Key2) ->
       %% insert two keys which will
  -    BaseKey = get_rnd_key(),
       H = histogram_rt:create(1, BaseKey),
  -    Key1 = get_rnd_key(),
  -    Key2 = get_rnd_key(),
       H2 = histogram_rt:add(Key1, H),
       H3 = histogram_rt:add(Key2, H2),
       %% check results
  
positive.code:         false -> SplitKey = ?RT:get_split_key(Key2, Key1, {1,2})
      end,
      ?equals(histogram_rt:get_data(H3), [{SplitKey, 2}]),
      ok.
  
  get_rnd_key() ->
      ?RT:get_random_in_interval({'[', ?MINUS_INFINITY, ?PLUS_INFINITY, ')'}).
  
  number_to_key(Val) ->
      ?RT:hash_key(erlang:integer_to_list(Val)).
negative.code: 
  all()    ->
      [
       add_keys,
       merge_keys
      ].
  
  suite() -> [ {timetrap, {seconds, 30}} ].
  
  init_per_suite(Config) ->
      unittest_helper:init_per_suite(Config).
  
  end_per_suite(Config) ->
      _ = unittest_helper:end_per_suite(Config),
      ok.
  
  -spec prop_add_keys(BaseKey::?RT:key(), Size::1..50, Values::[?RT:key(),...]) -> true.
  prop_add_keys(BaseKey, Size, Values0) ->
      H = histogram_rt:create(Size, BaseKey),
      Values = lists:sublist(Values0, Size),
      H2 = lists:foldl(fun histogram_rt:add/2, H, Values),
      %% check results
      SortedValues = lists:sort(fun(Val, Val2) ->
  