anchor.diff:           postcondition/3]).
   
   
  --type db_type() :: 'bitcask' | 'leveldb'.
  +-type db_type() :: 'bitcask' | 'leveldb' | 'ets'.
   
   -record(state, {stored = []  :: [string()],  %% list of objects stored in DB
                   type         :: db_type()
  
positive.code:                     begin
                          leo_backend_db_api:new(?INSTANCE_NAME, ?NUM_OF_PROCS, Type, ?DB_PATH),
                          {H,S,Res} = run_commands(?MODULE, Cmds),
                          ?debugVal({H,S,Res}),
  
                          leo_backend_db_api:stop(?INSTANCE_NAME),
                          application:stop(leo_backend_db),
  
negative.code:     oneof(Cmd0).
  
  
  %% @doc Pre-Condition
  %%
  precondition(_S, {call,_,_,_}) ->
      true.
  
  
  %% @doc Next-State
  %%
  next_state(S, _V, {call,_,put,[_Instance, Key, _Object]}) ->
      %% ?debugVal(_V),
      case proplists:is_defined(Key, S#state.stored) of
          false ->
              S#state{stored = S#state.stored ++ [Key]};
  