anchor.diff:                  _oneTimeListeners[event].clear();
               }
           }
  +
  +        return this;
       }
   
  -    void setMaxListeners(int listenersCount) {
  +    EventEmitter setMaxListeners(int listenersCount) {
           _maxListeners = listenersCount;
  +
  +        return this;
       }
   
       List listeners(String event) {
  
positive.code:         if (_oneTimeListeners.containsKey(event) && _oneTimeListeners[event].contains(listener)) {
              _oneTimeListeners[event].remove(listener);
          }
      }
  
      void removeAllListeners([String event]) {
          if (event == null) {
              _listeners.clear();
          } else{
  
negative.code:         return result;
      }
  
      bool emit(String event) {
          bool handlersFound = false;
  
          if (_listeners.containsKey(event)) {
              handlersFound = true;
              _listeners[event].forEach((Function handler) {
                  handler();
              });
          }
  
          if (_oneTimeListeners.containsKey(event)) {
              handlersFound = true;
              for (int i = 0; i < _oneTimeListeners[event].length; i++) {
                  Function handler = _oneTimeListeners[event][i];
                  handler();
                  _oneTimeListeners[event].removeAt(i);
              }
          }
  
          return handlersFound;
      }
  
      static int listenerCount(EventEmitterInterface emitter, String event) {
  