anchor.diff:  -spec end_per_testcase(atom(), serpents_test_utils:config()) ->
     serpents_test_utils:config().
   end_per_testcase(JoinGameTest, Config)
  -  when JoinGameTest == join_game_ok; JoinGameTest == join_game_wrong ->
  +  when JoinGameTest == join_game_ok
  +     ; JoinGameTest == join_game_wrong ->
     lists:filter(
       fun ({K, _}) -> not lists:member(K, [game, player1, player2, player3]) end,
       Config);
  
positive.code:         , game_creation_bad_cols/1
          , join_game_ok/1
          , join_game_wrong/1
          ]).
  
  -spec all() -> [atom()].
  
negative.code: -spec init_per_testcase(atom(), serpents_test_utils:config()) ->
    serpents_test_utils:config().
  init_per_testcase(JoinGameTest, Config)
    when JoinGameTest == join_game_ok
       ; JoinGameTest == join_game_wrong ->
    Game = serpents_core:create_game(#{cols => 10, rows => 10}),
    Player1 = serpents_core:register_player(<<"1">>),
    Player2 = serpents_core:register_player(<<"2">>),
  