anchor.diff:  key() ->
       oneof([a, b, c, d, e, f, g]).
   
  +real_any() ->
  +    %% ensure maps are tested!!!
  +    weighted_union([{1, map(any(), any())},
  +                    {10, any()}]).
  +
   %% Abstract state machine
   initial_state() ->
       #{vars => [], envs => []}.
   
   command(_S) ->
       oneof([
  -              {call, ?MODULE, set_app_env_variable, [key(), any()]},
  +              {call, ?MODULE, set_app_env_variable, [key(), real_any()]},
                 {call, amoc_config_env, get, [key()]},
  -              {call, amoc_config_env, get, [key(), any()]},
  -              {call, ?MODULE, set_env_variable, [key(), any()]}
  +              {call, amoc_config_env, get, [key(), real_any()]},
  +              {call, ?MODULE, set_env_variable, [key(), real_any()]}
             ]).
   
   %%
  
positive.code: %% statem helpers
  set_env_variable(Name, Value) ->
      EnvName = env_name(Name),
      true = os:putenv(EnvName, lists:flatten(io_lib:format("~p", [Value]))),
      ok.
  
  set_app_env_variable(Name, Value) ->
  
negative.code: -compile(export_all).
  
  all() ->
      [%test_any_type,
       config_prop_test].
  
  test_any_type(_Config) ->
      ProperTest = ?FORALL(Value, any(), not is_map(Value)),
      ?assertEqual(true, proper:quickcheck(ProperTest, [long_result, 10000, quiet])).
  
  config_prop_test(_Config) ->
       ?assertEqual(true, proper:quickcheck(config_prop(), [long_result, 1000, quiet])).
  
  config_prop() ->
      ?FORALL(Cmds, proper_statem:commands(?MODULE),
  