anchor.diff:          ?_assertEqual(deep_merge([First, Second]), deep_merge(First, Second))
       ]}.
   
  -deep_merge_fun_() ->
  +deep_merge_fun_test_() ->
       First = #{a => [1, 2], b => #{c => [a]}},
       Second = #{a => [3, 4], b => #{c => [b]}},
       Fun = fun(A, B) -> A ++ B end,
  
positive.code:         )
      ] ++ error_(fun(P, M) -> deep_update(P, 2, M) end)}.
  
  deep_update_with_() ->
      Incr = fun(V) -> V + 1 end,
      {inparallel, [
          ?_assertEqual(#{a => 2}, deep_update_with([a], Incr, #{a => 1})),
  
negative.code:         )
      ]}.
  
  deep_merge_test_() ->
      [First, Second|_] = Maps = [
          #{val => 1, a => 1},
          #{val => 2, b => 2, x => #{2 => true, y => #{more => stuff}}},
  