anchor.diff:      Action = impl_func_to_action_name( Func ),
       handle_impl_result( Result, Action, State, Tag ).
   
  +handle_impl_result( { ok, Context }, code_change, State, _Tag ) ->
  +    NewState = State#state{ context = Context },
  +    { ok, NewState };
  +
  +handle_impl_result( { error, _ } = Result, code_change, _State, _Tag ) ->
  +    Result;
  +
   handle_impl_result( { ok, Result, Context }, Action, State, Tag ) ->
       NewState = State#state{ context = Context },
       send_owner( NewState, Action, { ok, Result }, Tag ),
  
positive.code:     ok.
  
  
  code_change( _OldVsn, State, _Extra ) ->
      % FIXME - call the implementation's code_change
      { ok, State }.
  
  
  %% ===================================================================
  
negative.code:       fun mock_impl_module_stop/1,
        [ fun test_start_device/1
        , fun test_get_event/1
        , fun test_code_change/1
        %, fun test_stop_device/1
        ]
      }.
  