anchor.diff:      [ logplex_token:cache(Token)
         || Token <- Tokens ],
       true = lists:sort(Tokens) =:=
  -        lists:sort(logplex_token:lookup_by_channel(Chan)).
  +        lists:sort(logplex_token:lookup_by_channel(Chan)),
  +    logplex_token:delete_by_channel(Chan),
  +    [] = logplex_token:lookup_by_channel(Chan).
  
positive.code: %%% TESTS %%%
  %%%%%%%%%%%%%
  
  lookup_by_channel(Config) ->
      Chan = ?config(chan, Config),
      Tokens = [ logplex_token:new(Chan, list_to_binary(Name))
                 || Name <- ["heroku", "app", "postgres", "bob"]],
  
negative.code: %% a single atom.
  
  all() ->
      [by_channel].
  
  %%%%%%%%%%%%%%%%%%%%%%
  %%% Setup/Teardown %%%
  